AS Level Past Paper Questions

Source address

Destination address

Reassembly information

Sequence and acknowledgement numbers / tracking information

Data itself (payload)

Checksum / error handling

Protocol type

Header length

Flags

Payload size

Network collisions occur when two sets of data are detected on the network simultaneously.

The collision detection process involves monitoring the network to identify when a collision occurs.

Once detected, a computer waits for a short (random) time then sends again.

Step 1: A·B + A·C + C·A + C·C + B·B + B·A

Step 2: A·B + A·C + C·A + C·C + B + B·A (since B·B = B)

Step 3: A·B + A·C + C·A + B + B·A (since C·C absorbs into other terms)

Step 4: B·(A + 1 + A) + A·C + C·A

Step 5: B + A·C + C·A

Step 6: B + A·(C + C)

Step 7: B + A·(1)

Step 8: B + A

The number of bits that can be processed as a single unit by the CPU.

27₁₀ = 00011011 7E₁₆ = 01111110

Carry: 111111

00011011

• 01111110

  10011001

Truncation: 101.0₂

Absolute Error: 0.3125₁₀ (the part removed: 0.0101₂)

Relative error: 0.3125 / 5.3125 = 0.0588 (approximately 5.88% or 6%)

Declare Subroutine ConvertLength length is real conversionType is string do output “Please input next length” input length if length >= 0 then if length = val(length) then output “Please input conversion type” input conversionType if conversionType = “cm” then set length = length * 2.54 output “Length in cm is”, length else if conversionType = “m” then set length = length * 0.0254 output “Length in m is”, length end if else output “Incorrect value entered” end if end if while (length > 0) End Subroutine

Marking: Declare/initialise variables, loop through values, input length, validation check with error message, input conversion method, correct conversion, output conversion, rogue value termination.

Fixed length records have the same number of bytes/characters in each record and the same number of fields. Variable length records have different numbers of bytes in each record or different numbers of fields.

Fixed length records are easier to program as you can calculate how much space is required. Variable length records make it difficult to calculate space requirements.

Fixed length records are quicker to process (read/write) as start and end locations are known. Variable length records are slower as locations must be calculated at read/write time.

Fixed length records waste storage space as fields have blank space. Variable length records save space as there is no blank space.

Fixed length records will truncate long fields. Variable length records avoid truncation as each field can extend to accommodate any number of characters.

Examples: Fixed length: Date of Birth, National Insurance Number, Telephone Number Variable length: Surname, Address

Sequential file access:

• Accessed by reading the file from beginning to end
• File access is quicker where many records need to be accessed (no need to use an index)
• No requirement for storage space for an index

Indexed sequential file access:

• Includes a separate index from the main data file
• The index contains information about the location of each record in the file
• Allows for direct access to specific records
• Faster access to individual records via the index, compared to simple sequential
• Periodically, the index would need to be reorganised

Access levels / rights — certain users would have different or restricted access to certain data or parts of the system.

Write-protect mechanisms — only certain users will have permission to write or edit data already stored on the system.

Unique username and strong secure password — the organisation limits access by ensuring all authorised users have unique credentials.

Encryption — unauthorised users are prevented from reading confidential files because the data is unintelligible / scrambled.

Firewall — servers are protected with firewall software blocking and checking all network traffic entering or leaving specified ports.

Antivirus software — regularly scans all files for possible infection by malware.

factor = 2 is the constant.

A constant is a fixed value used in an algorithm that remains unchanged throughout the execution of the program.

i or num — A placeholder used to store and manipulate data. Its value changes during program execution.

if i MOD 2 = 0 — Execute a set of instructions if a condition is met.

while (i <= 10) — Repeatedly execute a set of instructions until a condition is met.

An object is an instance of a class. It represents a specific occurrence of a class with unique properties and behaviours.

A class is a template for an object. Classes define an object’s attributes and methods. An object may inherit methods and attributes from a class.

Person

Pupil or Staff

getEmergencyContact() : String

or getStaffID() : Integer

Public (+) — Any class can access the attribute or call the method.

Private (-) — Only the current class will have access to the attribute or method.

Protected (#) — Only the current class and its subclasses will have access to the attribute or method.

Step-by-step tutorials for the main features of the system

Guide on how to install software

Licence information

Reference manual

Online help at the level of both individual controls and at the task level

Error messages and trouble-shooting guide

Frequently asked questions (FAQs) detailing common questions and problems

Glossary

Diagrams used in analysis and design

Descriptions of procedures and subroutines used

Data structures — what data structures have been used, database table designs

Algorithm designs — presented in pseudo-code or flowchart form

Annotated code listings — self-documenting and/or annotated code

Variable lists — key variables listing data types and purpose

Data dictionary — describing all fields including data type, size, relationships

Design documents from the design phase

Hardware and software requirements (performance, storage, networking, compatibility)

Configuration guide and options

Editor — allows a programmer to enter and edit source code and annotation.

Interpreter — translates each line of source code and executes it.

Automatic formatting — correctly indents code.

Automatic colour coding — changes keywords, variables, literals and annotation to different colours.

Linker — allows previously compiled code from software libraries to be linked together.

Loader — loads previously compiled code into memory.

Debugger — helps locate, identify and rectify errors in a program.

Trace — displays the order in which lines are executed and possibly variable values.

Break point — interrupts a program on a specific line, allowing the programmer to compare variable values against expected values. Code can then be single-stepped.

Variable watch — displays the current value of any variable during execution.

Memory inspector — displays the contents of a section of memory.

Lexical analysis is the first phase of compilation, performed by a program known as the lexer.

It converts the high-level code into a sequence of tokens. Redundant parts of the source code, such as comments and unneeded spaces, are removed.

A symbol table is created to provide the compiler with quick access to the contents of the source code. Information about identifiers, arrays, parameters and subroutines is stored in the symbol table.

As the lexer works through the source code, it checks if each lexeme already exists in the symbol table — if not, a new entry is added.

The output is a sequence of tokens sent to the parser for syntax analysis.

Semantic analysis is the third stage of compilation.

Variables are checked to ensure they have been properly declared, used and are within scope by checking against the symbol table.

Variables are checked to ensure they are of the correct data type, e.g. real values are not being assigned to integers.

Tokens are checked for any misuse of reserved identifiers.

Operations are checked to ensure they are legal for the type of variable being used.

If statements are checked to ensure they can evaluate whether the condition is true or false. Exit conditions for loops are similarly evaluated.

User Interface:

• Provides graphical user interface with meaningful icons, drop-down menus
• Can provide a command line interface
• Allows customisation (desktop colours, layout)
• Allows access to system settings such as hardware
• Allows copying, deleting, moving, sorting, searching of files or folders
• Controls security using passwords or access permissions
• Allows switching between tasks and multiple windows
• Provides error, warning and help messages

Managing Resources:

• Communicates with output devices (printer, monitor) and input devices (keyboard, mouse)
• Spooling — data is stored in a queue/buffer for printing
• Manages backing store — ensures data is stored and retrieved correctly, creates filing systems (FAT, NTFS), organises files in hierarchical directory structures
• Offers compression to save disk space
• Manages RAM — ensures programs and data are stored in correct memory locations and don’t occupy the same location
• Can utilise virtual memory when insufficient RAM is available
• Ensures different processes can utilise the CPU without interfering with each other
• On a multi-tasking OS, ensures all tasks appear to run simultaneously

Award 1 mark for each correct cell, max 6.

Character maps are used to represent each character.

Each character is mapped to a binary number.

Allows for standardised communication between computer systems.

Four instructions can be processed at the same time / simultaneously.

Step 1: Each core processes one multiplication: 4×5=20, 1×6=6, 5×3=15, 3×2=6

Step 2: Two cores add pairs: 20+6=26, 15+6=21

Step 3: One core adds the results: 26+21=47

Parallel processing

Control Unit — Directs the flow of instructions and/or data; coordinates the other parts of the CPU; generates clock ticks or controls the clock.

Arithmetic Logic Unit (ALU) — Performs all the mathematical calculations and logical operations in the CPU.

Registers — Fast access temporary storage to store frequently used data and instructions.

Cache memory — Smaller, faster memory closer to the processor core; stores copies of data from frequently used main memory locations.

Other valid components: MDR (holds data to be stored or fetched), MAR (holds memory address of data to be accessed), Accumulator (stores intermediate ALU results), CIR (holds currently executing instruction), PC (indicates where in the program sequence), Buses (connect different parts of CPU).

Mask: 10000000 Logical Operation: AND Result: 10111000 AND 10000000 = 10000000

The result is non-zero (10000000), so the most significant bit is 1.

When data is fragmented it is split and stored on different parts of the disk.

HDD uses magnetic secondary storage technology which is impacted by fragmentation. Data is stored on a hard drive platter.

Data is read using an arm that has a special read/write head at the end. As the disk spins, the arm travels across the disk.

Fragmentation will slow access speeds as the read/write head will need to move into several different positions at each point where the data is split.

Defragmentation — where fragmented data is physically rearranged and stored closer together on disk, meaning the read/write head will need to move into fewer different positions.

When a computer system establishes a device’s readiness to communicate.

Ensures that hardware and software produced by different vendors can work together.

Without networking standards, it would be difficult or impossible to develop networks that easily share information.

Standards mean that customers are not locked into one vendor.

Standards help to promote more competition and hold down prices.

The use of standards makes it much easier to develop software and hardware that link different networks because software and hardware can be developed one layer at a time.

Protocol 1: File Transfer Protocol (FTP) Function: Allows the transfer of files over a network. Importance: FTP has in-built error checking and re-transmission request as necessary.

Protocol 2: Hypertext Transfer Protocol (HTTP) Function: Allows the transfer of multimedia webpages over the internet. Importance: HTTP allows multiple different web browsers to display and format web pages as the original author intended.

Other valid protocols: SMTP (email sending), IMAP (email retrieval, server-side storage), DHCP (dynamic IP address assignment), UDP (datagram delivery with minimal overhead, suitable for streaming), TCP/IP (allows any networked computers to communicate, specifies signal routing).

Simplex:

• Data can only travel in one direction.
• Example: Keyboard (data only flows from keyboard to computer).

Half duplex:

• Data can travel in both directions but only in one direction at any given time.
• Example: Walkie-talkie (one person speaks while the other listens, then they swap).

Full duplex:

• Data can travel in both directions at the same time.
• Example: Broadband internet connection (can upload and download simultaneously).

declare r as real declare area as real declare circumference as real declare pi as real

set pi = 3.14

input r

if r > 0 then area = pi * r * r area = area * 10000 circumference = 2 * pi * r circumference = circumference * 100 output “A = “, area output “C = “, circumference else output “You must enter a number > 0 for r.” end if

Marking: Declare/initialise variables, input r, validation check on r, calculation of area in cm², calculation of circumference in cm, output area, output circumference, output validation error message.

Q·(P + Q) + P·(1 + R) + Q·(P·P̄)

Step 1: Q·(P + Q) + P·(1 + R) + Q·0 [since P·P̄ = 0]

Step 2: Q·(P + Q) + P·(1 + R) [since Q·0 = 0]

Step 3: Q·P + Q·Q + P·1 [expanding brackets; 1+R = 1]

Step 4: Q·P + Q + P·1 [since Q·Q = Q]

Step 5: Q·P + Q + P [since P·1 = P]

Step 6: Q·(P + 1) + P [factoring Q]

Step 7: Q + P [since P + 1 = 1, so Q·1 = Q]

1st: 1, 2nd: 2, 3rd: 5, 4th: 6, 5th: 8, 6th: 11, 7th: 14

1st: 6 (middle element at index 3), 2nd: 11 (middle of upper half, index 5), 3rd: 14 (index 6, found)

Advantage: A binary search has better time performance than a linear search (the data to be searched halves with each step, so it is logarithmic).

Disadvantage: The data must be sorted before a binary search can be used. Also more complex to code than linear.

Data compression reduces the file size.

Lossy data compression:

• Some of the original data is discarded to reduce the size of the file.
• When compressed files are decompressed they do not give back the original data (data is lost).
• Not a good method for critical data such as textual data.
• Most useful for digitally sampled analogue data such as sound, video, graphics or images.

Lossless data compression:

• The original message can be decompressed back to its original form (recovers all original data).
• Works by finding repeated patterns in data and compressing those patterns efficiently (e.g. Huffman encoding).
• Also referred to as redundancy reduction.
• Does not work well on random messages (dependent on patterns).
• Ideal for text.

A data structure is a group/set/collection of related records.

It provides a convenient and efficient way of organising data relating to a real problem, and may be efficient to deal with various elements as one item.

Example: FilmID / Title / Certificate / Genre.

Description: A field is a collection of related data (a single piece of information about an entity).

Example: 1, End in Justice, 18, Horror (or any complete row from the table).

Description: A record is a collection of fields all related to a single entity.

Example: FilmID.

Description: A primary key is a unique identifier for each record.

Sequential files order records based on a primary key field.

In order to add a new record, the position in the file where the record is to be added must be found.

It is not possible to move records about easily within a file due to the serial nature of files.

This means that any inserting or deleting from sequential files must happen in a temporary file.

When inserting, records are copied from the original file into a temporary file. This continues until the point where the new record is to be inserted is found.

At this point the new record is added to the temporary file and the remainder of the old file is copied over.

The temporary file then replaces the original file.

Adaptive maintenance: Bugs are fixed and extra functionality is added to the system based on external needs. For example, changes in the law may require new features (e.g. cookie compliance).

OR Corrective maintenance: Fixes problems as they arise to ensure the system closely matches the original specification. The developer works on fixing problems without breaking the system or adding functionality.

OR Perfective maintenance: Maintenance performed with the aim of achieving a perfect system — fixing all problems, implementing new or changed requirements, and improving performance.

Method 1 (8-bit integer): Highest: 01111111₂ = 127₁₀ Lowest: 00000000₂ = 0₁₀

Method 2 (5-bit mantissa, 3-bit exponent): Highest: Mantissa 0.1111, Exponent 011 (3) → 7.5₁₀ Lowest: Mantissa 0.1000, Exponent 000 or 101 → 0.5₁₀ or 0.0625₁₀

Method 3 (4-bit mantissa, 4-bit exponent): Highest: Mantissa 0.111, Exponent 0111 (7) → 112₁₀ Lowest: Mantissa 0.100, Exponent 0000 or 1100 → 0.5₁₀ or 0.125₁₀

Advantages of integers:

• Numbers are stored accurately
• Less complex processing
• Exact representation of zero
• Less storage space

Advantages of floating-point:

• Very large or very small numbers can be stored
• Larger range of numbers can be represented
• Fractions / decimal places can be represented

Fetch:

• The address of the next instruction is copied from the PC to the MAR.
• The instruction is copied from RAM to the MDR.
• The PC is incremented so that it holds the address of the next instruction.

Decode:

• The MDR contents are copied into the Current Instruction Register (CIR).
• The instruction (opcode) is decoded.
• The operand (if required) is also decoded or fetched from RAM.

Execute:

• The instruction is carried out.
• Each stage is designed to happen concurrently to maximise resource use (clock ticks and memory).

Voice input uses a microphone. Voice driven interfaces (voice recognition) can be used to issue commands to a computer system and enter data.

Benefits:

• Speech input is much faster than keyboard input
• No need to learn to type; less danger of RSI
• Natural way for people to communicate
• Hands-free advantages — can multitask
• Users with disabilities that prevent typing can use speech input

Drawbacks:

• Background noise interferes with speech recognition
• Users with speech impediments, sore throats, colds, or strong accents may not be understood
• Difficult to keep data input private as people can hear what you say
• Words that sound the same (e.g. ‘too’ and ‘two’) may not be recognised correctly

Touch screens (normally capacitive touch) work on the principle that the human body is an electronic conductor. When you press on a capacitive screen it distorts the electromagnetic field, measured as a change in capacitance, translated into x and y coordinates.

Benefits:

• Touch screens allow for intuitive gestures (e.g. swipe, pinch to zoom)
• Very intuitive — user simply touches what is seen on the display
• No keyboard or mouse required
• Easier hand-eye coordination than mice or keyboards

Drawbacks:

• Screen can be easily damaged/scratched
• Dirty screens are difficult to read
• Users must be within arm’s reach of the display
• Difficult to select small items; user’s hand may obscure the screen
• Some reduction in image brightness may occur

Multiplexing is where several independent data sources are combined to be sent along a single route to a specific destination.

Source address — allows tracing of the sender.

Destination address — allows the packet to be routed to its destination.

Reassembly information / packet number — allows packets to be assembled in the correct order.

Tracking information — allows the route taken to be traced.

The data itself — the packet contains meaningful payload data.

Checksum — allows checking of data for errors.

The number of bits that can be processed as a single unit by the processor.

AE₁₆ = 10101110₂ 1B₁₆ = 00011011₂

Binary addition: 10101110

• 00011011

  11001001 Carry: 01111100

11001001₂ = 201₁₀

Sign/magnitude: 10100111₂

Two’s complement: 11011001₂

Mantissa = 0.90625₁₀

Exponent = 2₁₀

Denary value = 3.625₁₀

Mantissa = 0.1111111₂ = 0.9921875₁₀

Exponent = 011₂ = 3₁₀

Largest positive number = 7.9375₁₀

Original: 111.10110₂ = 7.6875₁₀

Truncation to 2 binary places: 111.10₂ = 7.5₁₀ Absolute error: 0.00110₂ = 0.1875₁₀

Rounding to 2 binary places: 111.11₂ = 7.75₁₀ Absolute error: 0.00010₂ = 0.0625₁₀

Rounding is more accurate (smaller absolute error).

Fixed length records have the same number of bytes in each record and the same number of fields. Variable length records have different numbers of bytes in each record or different numbers of fields.

Fixed length records are easier to program as you can calculate how much space will be required. Variable length records make it difficult to calculate space requirements.

Fixed length records are quicker to process (read/write) as start and end locations are known. Variable length records are slower as locations must be calculated at read/write time.

Fixed length records waste storage space as fields have blank space. Variable length records save space as there is no blank space.

Fixed length records will truncate long fields. Variable length records avoid truncation as each field can extend to accommodate any number of characters.

Different user groups can have different views / access rights / privileges:

• Improves security
• Certain fields or tables can be hidden
• Certain fields or tables can be visible but read-only, preventing unauthorised editing
• Users can be restricted from running queries
• Users can be restricted from altering the database structure
• Users can be restricted from deleting records

A pre-defined complicated query can be made available for users to view. Views can be set up with performance in mind and re-used by other developers. A certain view can simplify access to data spread over multiple tables.

Files can be archived when they are no longer in use but may be needed at some point in the future.

declare loginDetails(3,5) as string set username as string set password as string set flag as Boolean set flag = FALSE output “Please enter username” input username output “Please enter password” input password for i = 0 to 4 if username = loginDetails(0,i) AND password = loginDetails(1,i) then output “You have successfully logged in “, loginDetails(2,i) set flag = TRUE else if username = loginDetails(0,i) AND password <> loginDetails(1,i) then output “Incorrect password” end if end if next i if flag = FALSE then output “User not found” end if

Marking: Initialise variables, input username and password, loop structure + increment, username comparison, password comparison, output successful message with full name, output error for incorrect password, output error for user not found.

Batch processing is the suitable mode of operation.

Time sheets or hours worked are collected. Data is collected over a period of time (weekly or monthly). The batch is processed at the end of that period.

The process is carried out with no user interaction. Batch processing may avoid using computer resources at times when demand is high (processed off-peak). Errors are stored in a file for later use and not dealt with as they occur.

Step 1: (Ā + B)·(A + C) + B·B̄ Step 2: (Ā + B)·(A + C) [since B·B̄ = 0] Step 3: Ā·A + Ā·C + B·A + B·C [expanding brackets] Step 4: 0 + Ā·C + B·A + B·C [since Ā·A = 0] Step 5: Ā·C + A·B + B·C Step 6: A·(1 + C + B) + B·C → simplified to A + B·C

Final answer: A + B·C

C (set to 3.14) is the constant.

A constant is a value that cannot be altered by the program during normal execution.

A or B is a variable.

A variable is an identifier with a value that can be changed during normal execution.

Self-documenting identifiers are meaningful, which allows other programmers to follow the code more easily.

Suggested changes:

• A → r or radius
• B → area
• C → pi

Procedural languages are used in traditional programming based on algorithms or a logical step-by-step process for solving a problem.

They obey ordered instructions and carry out actions/calculations.

A procedural programming language provides the programmer a way to define precisely each step when performing a task.

Allows tight control over the underlying operation of the hardware.

Used in large complicated programs where similar operations may be carried out at varying stages of the program execution.

Mark-up languages add commands, or mark-up, to a text document to offer meaning to the text.

The commands give instructions to the program reading the file on how to interpret and display the text.

One of the most common mark-up languages is HTML. Commands in HTML are called tags and are surrounded by chevrons. Commands are opened (e.g. <h1>) and closed using a forward slash (e.g. </h1>).

XML (eXtensible Mark-up Language) is another mark-up language commonly used in web applications, for structuring and marking-up data for storage rather than display. Developers can create their own tags and specify their own meaning.

Mark-up languages are commonly combined with other languages, such as JavaScript with HTML.

Malicious damage is when data is amended or deleted on purpose. Example: A hacker could access and change data or plant a virus; a disgruntled employee could damage data intentionally.

Accidental damage is when data is amended or deleted without malicious intention. Example: An employee deleting information by accident; a computer server crash or system failure; computer damage due to fire or flood.

Using a knowledge-based system, a user can interrogate a vast knowledge base to find a solution. The user enters information they already have, and the knowledge-based system infers an answer. If the system cannot reach a conclusion, it requests more information, continuing until it either has high confidence in a solution or has exhausted every line of inquiry.

Advantages:

• The computer can store far more information than a human, drawing on stored knowledge from books and case studies
• The computer does not forget or make mistakes
• Data can be kept up-to-date
• The expert system is always available 24 hours a day and will never retire
• Can be used at a distance over a network, giving rural or developing areas access to expertise
• Provides accurate predictions with probabilities
• Some people prefer the privacy of talking to a computer

Disadvantages:

• Over reliance upon computers
• Some employees could be de-skilled by over dependence on computer advice
• Fewer staff could be needed (impact on employment)
• Lacks the ‘human touch’ — lack of personal contact
• Dependent on correct information being given; wrong data or rules lead to wrong advice
• No human available if you do not know what to do

The Internet is a world-wide communications infrastructure / a network of networks.

Sending datagrams across a network with very few error recovery services. Used for streaming multimedia.

Assigning dynamic IP addresses to devices on a network.

Sending an email across a network / internet. Used to send email to an email server.

a = 0

b = 1

c and d will not output (undefined / null / error) because they are local to myFunction and out of scope in the main program.

The algorithm will not output c or d (they will be blank/null/undefined/random data).

This is because the scope of c and d lies within the function myFunction — c and d are local variables to myFunction.

The lifetime of the data stored in each variable ends when myFunction ends.

c and d are not available to the main program.

Control Unit — Directs the flow of instructions and/or data; coordinates the other parts of the CPU; generates clock ticks or controls the clock.

Arithmetic Logic Unit (ALU) — Performs all the mathematical calculations and logical operations in the CPU.

Registers — A small amount of fast access storage, normally used for a specific purpose where data or control information is temporarily stored.

Other valid components: MDR (holds data to be stored or fetched from RAM), MAR (holds memory address of data to be accessed), CIR (holds currently executing instruction), PC (indicates position in program sequence), Cache memory (smaller, faster memory closer to processor core storing frequently used data).

Hard drives have a fast transfer rate and fairly fast access time.

Hard drives are a magnetic medium and store data on a hard drive platter.

Data is read and saved using an arm that has a special read/write head at the end.

As the disk spins, the arm travels across the disk.

Each sector of the platter can store data, and the movement of both the disk and the read/write head means every sector can be reached.

The faster the platter spins, the faster data can be read (measured in RPM — a common speed is 7200 RPM).

The fragmented file is split and stored on different parts of the disk. When data is fragmented, it takes longer for the disk heads to move between parts of the file, which slows the process of loading it.

An SSD uses direct access to data (files). There would be no deterioration in read times as there is no physical read-head to move.

C = A·B̄ (or C = A AND NOT B)

The output is 1 only in the row where A = 1 and B = 0.

Note: this entry previously recorded the table with A and B transposed, and gave the answer as Ā·B. The paper prints the rows with A varying fastest — 0 0, 1 0, 0 1, 1 1 — so the row with output 1 is A = 1, B = 0.

R = P̄·Q̄ (or R = NOT P AND NOT Q, equivalently R = NOT(P OR Q) / NOR)

Z = (X ⊕ Y)̅ (XNOR — the output is 1 when X and Y are equal)

Equivalently Z = X̄·Ȳ + X·Y, or Z = NOT(X XOR Y).

Note: this entry previously gave the answer as Z = X ⊕ Y, which is XOR — the complement of this table — while its own parenthetical said XNOR.

A parameter is a variable/value that can be passed to/from a procedure.

When passing by reference, the address of the required data is passed to the procedure (rather than the actual value of the data).

Passing by value — where a local copy of the data is created for the procedure (and discarded when the procedure ends).

Passing by reference may lead to unintended side effects where the parameter has its value changed in the procedure, which then inappropriately affects its value in the main program.

Two input files: old master file and sorted transaction file.

Update process: comparison — transaction records are compared record by record with corresponding master records to update the master.

New (updated) master file is output.

Document output (e.g. bill, payslip) is also produced.

flowchart LR
    OM[("Old master file")] --> UP["Update process:<br>compare records"]
    TF[("Sorted transaction file")] --> UP
    UP --> NM[("New master file")]
    UP --> DOC["Printed document<br>e.g. bill, payslip"]

Transaction files use serial organisation — records are stored in no particular or chronological order.

Master files use sequential organisation — records are stored in order by key field.

Example (Payroll):

• Transaction file: hours worked for each employee
• Master file: employee details and pay details to date

Example (Utility bill):

• Transaction file: meter readings
• Master file: customer details and utility usage to date

Batch processing.

The process is carried out with no user interaction. Batch processing may avoid using computer resources at times when demand is high (processed off-peak). Errors are stored in a file for later use and not dealt with as they occur. Data is collected and processed in one single operation.

A·(B + C) + A·(0 + Ā) + B·(1 + C)

Step 1: A·B + A·C + A·0 + A·Ā + B·1 + B·C [expanding brackets]

Step 2: A·B + A·C + 0 + A·Ā + B + B·C [A·0 = 0, B·1 = B]

Step 3: A·B + A·C + A·Ā + B + B·C [removing 0]

Step 4: A·B + A·C + B + B·C [A·Ā = 0]

Step 5: B·(A + 1 + C) + A·C [factoring B]

Step 6: B + A·C [since A + 1 + C = 1]

File backup — A data backup is a copy or archive of files and folders for the purpose of being able to restore them in case of data loss. Autosaving of files as you use them (e.g. Word keeping backup copies).

Generations of files — Storage of three of the most recent versions of master file (grandfather-father-son). Useful if one version is corrupted; previous versions are still available. Data should be stored off-site in case of disaster.

Transaction logs — An incremental file security method. In order to restore a database to a certain point-in-time, all transaction log records are required to replay database changes. Only backs up data that has changed. Saves storage space and is faster than full backup.

Access Rights — Users can be given rights to certain files or file structures that prevent them from accessing, changing, or deleting them. File attributes can also be set.

Repetition 1: mid = (0+10) DIV 2 = 5, myArray[5] = 54. 22 < 54, so end = 4. Discard indices 5-10.

Repetition 2: mid = (0+4) DIV 2 = 2, myArray[2] = 27. 22 < 27, so end = 1. Discard indices 2-4.

Repetition 3: mid = (0+1) DIV 2 = 0, myArray[0] = 12. 22 > 12, so start = 1. Discard index 0.

Now mid = 1, myArray[1] = 22. Found!

declare myArray[1 to 5] set searchValue as integer set found as Boolean set found = FALSE set myArray = [45, 12, 98, 54, 56] input searchValue

for i = 1 to 5 if searchValue = myArray[i] then set found = TRUE output “SearchValue found at position “, i end if next i

if found = FALSE then output “SearchValue not found” end if

Marking: Declare and initialise variables, input searchValue, loop structure and increment, determine position if found, output position if found, correct terminating condition, output message if not found, algorithm works as intended.

Linear: Can be used on any set of data regardless of type and whether or not it is sorted. Suitable when the number of data items is low.

Binary: When the data is always sorted. Suitable when the number of data items is high.

6C₁₆ = 01101100₂ AF₁₆ = 10101111₂

01101100

• 10101111

  100011011₂

With unsigned exponent: Minimum: Mantissa 0.100, Exponent 0000 (0) → 0.5 × 2⁰ = 0.5₁₀ Maximum: Mantissa 0.111, Exponent 1111 (15) → 0.875 × 2¹⁵ = 28,672₁₀

With signed (two’s complement) exponent: Minimum: Mantissa 0.100, Exponent 0000 (0) → 0.5 × 2⁰ = 0.5₁₀ Maximum: Mantissa 0.111, Exponent 0111 (7) → 0.875 × 2⁷ = 112₁₀

Advantages of integers:

• Numbers are stored accurately
• Less complex processing
• Exact representation of zero
• Less storage space

Advantages of floating-point:

• Very large or very small numbers can be stored
• Larger range of numbers can be represented
• Fractions / decimal places can be represented

Consulting current documentation — to investigate current data storage requirements or data flow.

Carry out a questionnaire of staff/customers — because they may be spread over a wide geographical area and there are many of them.

Interview staff/customers/employees — suitable when the analyst requires a lot of information from a small number of people.

Observing the current system in practice — suitable for gathering information first-hand without having to rely on what people say is happening.

Research similar systems — desktop research looking at existing similar systems that are available.

Relational database features:

• Supports relationships: one-to-one, one-to-many
• Data is normalised
• Uses a primary key in each table as a unique identifier
• Uses a foreign key (primary key from another table) to form links between tables

Advantages:

• Avoids data duplication
• Minimised data inconsistency
• Easier to change data and data format
• Data can be added and removed easily
• Easier to maintain security
• Easier to back-up data and restore/recover from disasters

Features:

• Carry out queries/searches
• Sort data
• Forms for data entry
• Generate reports
• Perform calculations using calculated fields
• Can ensure reasonableness of data using validation
• Can ensure data consistency using verification

Security:

• Users can have different views
• Standard clerical procedures
• Passwords for access
• Write-protect mechanisms

Assigns dynamic IP addresses to devices on a network.

Internet standard for electronic mail (email) transmission.

Transfers webpages over a network.

Hacking — gaining unauthorised access to data or a computer system.

Virus — a program capable of copying itself with a detrimental effect such as corrupting the system or destroying data.

Trojan — a program designed to breach security while ostensibly performing an innocuous function.

Worm — standalone malware that replicates itself to spread to other computers.

Spyware — software that obtains information about another’s activities by transmitting data from their hard drive.

Botnets — a network of private computers infected with malicious software, controlled as a group (e.g. to send spam).

Keylogger — records every keystroke to gain fraudulent access to passwords.

Malicious damage — intentional corruption or deletion of files.

Accidental damage — unintentional corruption or deletion.

Loss of data leading to damage to company reputation, fines, or prosecution (GDPR).

Hardware failure leading to data loss.

ID theft leading to personal losses or fraud.

Levels of permitted access — certain users have different/restricted access to certain data.

Write-protect mechanisms — only certain users can write/edit data.

Strong secure password — limits access by ensuring authorised users have strong passwords.

Access rights — limits access to confidential files to authorised users only.

Encryption — prevents hackers reading confidential files by encrypting them.

Firewall — blocks/checks all network traffic entering or leaving specified ports.

Antivirus software — regularly scans files for possible infection by malware.

Backups — copies of data held in order to restore in event of data loss.

Policies/Legislation — relevant company policies and current legislation.

Accounting or auditing software — records all files accessed by a user in an activity log.

A·(Ā + B) + C̄·(A + B) + A·(B̄ + C) + B̄·B

Step 1: A·(Ā + B) + C̄·(A + B) + A·(B̄ + C) [B̄·B = 0]

Step 2: A·Ā + A·B + C̄·A + C̄·B + A·B̄ + A·C [expanding]

Step 3: 0 + A·B + C̄·A + C̄·B + A·B̄ + A·C [A·Ā = 0]

Step 4: A·(B + B̄) + C̄·A + C̄·B + A·C [factoring A]

Step 5: A·(B + B̄) + A·(C̄ + C) + C̄·B [factoring A]

Step 6: A·1 + A·1 + C̄·B

Step 7: A + C̄·B

Step 8: A + B·C̄

31₁₆ = 00110001₂ 6D₁₆ = 01101101₂

00110001

• 01101101

  10011110₂

16.125₁₀ = 10000.001₂

Normalised: Mantissa = 0.10000001000, Exponent = 0101 (5₁₀)

Mantissa = 0.1111₂ = 0.9375₁₀

Exponent = 011₂ = 3₁₀

Answer = 0.9375 × 2³ = 7.5₁₀

Two-dimensional array. It is appropriate because there is only one data type required (all values are integers).

Integer

Record — because it can store more than one data type and all data relates to a single entity.

Parallel processing:

• A form of computation in which many calculations are carried out simultaneously
• Uses multiple cores
• Large problems can often be divided into smaller ones, which are then solved concurrently
• More complex to design and write than sequential programs
• Communication and synchronisation between subtasks are obstacles to efficient performance

Cache memory:

• Similar to RAM but resides on or close to the CPU
• Faster than RAM and also volatile
• Used to store frequently used data from main memory
• Used by the processor to avoid slowing down to the speed of RAM
• Different levels of cache (L1, L2) denoting speed and characteristics
• Helps solve the Von Neumann bottleneck

Declare Subroutine ConvertCurrency amount is real output “Please enter the amount you wish to purchase in pounds” input amount if amount = val(amount) then for i = -5 to 5 output “£”, amount + i, “ = €”, (amount + i) * 1.14 next i else output “The value entered must be a number” end if End Subroutine

Marking: Declare/initialise variable, input amount, validation and error message, loop for numbers below amount, loop for numbers above amount, correct conversion, output conversion, correct formatting.

Binary search:

• Starts with the middle element of the array
• If the search item is not found, searches the lower or upper half depending on comparison
• Repeats until found or not present

Linear search:

• Starts at the beginning of the array
• The search item is compared to every consecutive item in the array
• Continues until either the item is found or the end of the array is reached

Binary search requires the input data to be sorted; linear search doesn’t.

Binary search requires an ordering comparison; linear search only requires equality comparisons.

Binary search requires random access to data; linear search only requires sequential access (can stream data of arbitrary size).

Linear search would be slower than binary search on a larger list.

Linear search is appropriate for data that cannot be sorted.

Test Data Set 1: Data with duplicates, e.g. 45, 32, 5, 32, 19, 62 Test Data Set 2: Already sorted ascending, e.g. 5, 19, 32, 35, 45, 62 Test Data Set 3: Already sorted descending, e.g. 62, 45, 35, 32, 19, 5

(Also valid: negative numbers, very large numbers, unsorted list)

A pass is made through the data, comparing each value with the following one and swapping them if necessary. A number of passes is made until the data is in order.

The variable ‘swapped’ will become TRUE after one swap, and the loop terminates when swapped = TRUE, so the loop will terminate too soon (after just one pass).

Alternatively: if the array is already in ascending order, swapped stays FALSE and the loop never terminates.

Change the terminating condition: Line 17 should be ‘until (swapped = FALSE)’ — the loop should terminate when no swaps are made in a pass.

Insertion sort — Comparisons are made, data is placed in the right position, and other items are moved along to make room.

Defragmentation — files are physically rearranged on disk so they are no longer fragmented and parts of each file are stored together.

Compression — software reduces file sizes using less space.

Task management — can see how much disk/CPU percentage a given program is using; can shut it down if dominating.

Disk scanning and repair — fixes problems on disk.

Anti-virus software — scans for viruses which could be causing issues with disk access speed or damaging data.

Firewall — prevents unauthorised network access.

Backup — allows users to archive files and delete files on hard disk to free up space.

Communicates with and sends data to output devices (printer, monitor) and receives input from devices (keyboard, mouse).

Manages network communication.

Spooling — data is stored on hard disk/in memory/in a queue/buffer for printing.

Manages backing store by ensuring data is stored and retrieved correctly from any disk drive.

Creates and maintains a filing system (FAT, NTFS) and organises files in a hierarchical directory structure.

Offers compression to save disk space.

Manages memory (RAM) — ensures all programs and data are stored in correct memory locations and don’t occupy the same location.

Can utilise virtual memory when insufficient RAM is available.

Ensures different processes can utilise the CPU without interfering with each other or crashing.

On a multi-tasking OS, ensures all tasks appear to run simultaneously.

Off-the-shelf:

• Cheaper — development costs spread across many users
• Available immediately — development already done
• Lower training costs — users may already be familiar
• Community support — books, forums, online communities
• More functionality — developers try to meet requirements of many users
• Upgrades included or at reduced cost
• Compromise — unlikely to do everything exactly as needed
• May be overly complicated with unnecessary features
• Not in control — vendor’s plans may not align with yours

Bespoke:

• Tailored to your specific requirements
• More flexible — can evolve over time
• No per-user fees if you own the software
• Not tied to a specific vendor
• Competitive advantage — competitors won’t have the same software
• Higher initial costs — you pay all development costs
• Takes longer — may take months or years to develop

A feasibility study establishes whether the project can be done given the scope defined. It considers whether it is desirable for the company to proceed — can the project be delivered on time and within budget.

Economic feasibility — considers overall budget and costs (software licences, hardware, human resources, wages, running costs). Decides if enough profit can be made.

Time feasibility — late projects go over budget due to developer wages. Project manager must estimate how long developers will take.

Technical feasibility — can the project be done with available technical resources? Some things are not feasible with current technology.

Political feasibility — projects may have politically motivated issues or go against beliefs of certain groups. Negative publicity must be weighed against positives.

Legal feasibility — helps decide whether the project can comply with all laws in countries where it will be released.

Computers in weather forecasting:

• Inputs from thousands of weather stations (satellites, balloons, ships) across huge geographical areas
• Requires processing huge amounts of data and comparison with historical data
• Requires very complex calculations
• Requires large, complex programs
• Processing must be very fast as forecasts are useless if out-of-date
• Weather is often extremely unstable/chaotic/hard to predict
• May require very good graphics for visual representation

Hard Disk Drive:

• Fast transfer rate and fairly fast access time, good compromise between capacity, performance and cost
• Magnetic medium, stores data on hard drive platters
• Data read/saved using an arm with a read/write head
• As the disk spins, the arm travels across the disk
• Each sector of the platter can store data
• Speed measured in RPM (common: 7200 RPM)
• Can be hybrid with SSD; fragmentation can slow access
• Typical use: Storing programs/OS/Server backup
• Typical capacity: 500MB – 4TB

Optical Drive:

• Uses lasers to store data by burning microscopic indentations into a disc
• Pattern created in a spiral from the middle; indentations create pits and lands
• A laser is aimed at the disc and reflected back
• DVD-ROM stores data on two layers with two lasers of differing wavelength
• Blu-ray stores pits and lands closer together using shorter wavelength (blue) laser
• Typical use: Movies/Music
• Typical capacity: 650MB – 128GB

Comparison: HDD has greater storage capacity, faster access speed; optical drives are more durable and portable.

A protocol is an agreed upon format (set of rules) which allows two devices to communicate / the transfer of data.

DHCP

SMTP

TCP/IP

When a computer system establishes a device’s readiness to communicate.

Collision. The transmitting node waits a random amount of time before trying to resend the packet.

Data is split into packets. Each packet has a destination address. Packets are analysed by each node and sent down the most appropriate path (lowest cost/traffic) to reach its destination. Each node maintains a routing table. Packets may take different routes. Packets are reassembled at their destination.

Storage requirements = 7 bits.

Example: 108₁₀ = 1101100₂

-63₁₀ to +63₁₀

Each character is mapped to a binary number.

Ensures that computers use the same character representation and can transfer meaningful data.

Unicode allows the storage of complex characters such as Chinese script and emojis.

Unicode can represent a larger range of characters than ASCII.

Character: e.g. ‘B’ = 8 bits (1 byte) String: e.g. ‘BOB’ = 24 bits (3 bytes)

A string requires storage for each character it contains.

Potential threats:

• Fire, flood, lightning, terrorist attacks
• Hardware failure (e.g. power supply unit failing)
• Software failure (e.g. virus damage)
• Accidental damage
• Malicious damage (e.g. hacking)

Contingency planning:

• Before the disaster: risk analysis, preventative measures and staff training to minimise data loss and ensure data can be recovered
• During the disaster: staff response — implement contingency plans to prevent further damage and begin immediate recovery
• After the disaster: recovery measures — purchasing replacement hardware, reinstalling software, restoring data from backups to restore normal running

A·(A + B) + C·(A + B) + A·(B + C)

Mark scheme derivation:

Step 1: Ā·A + Ā·B + C·A + C·B + A·B + A·C [expanding]

Step 2: 0 + Ā·B + C·A + C·B + A·B + A·C [Ā·A = 0]

Step 3: B·(Ā + A) + A·C + B·C [factoring B]

Step 4: B + A·C + B·C [Ā + A = 1]

Step 5: B + A·C [absorption: B + B·C = B]

Note: this working only holds if the first term carries a NOT bar that the question text is missing — WJEC draws the bar as a vector line, which text extraction drops. The S17 AS Unit 1 question paper was not available to confirm the intended expression, so the question has been left as extracted and this answer flagged rather than rewritten.

The recorded mark scheme ended at B + C. That does not follow from step 4: B + B·C absorbs to B, leaving B + A·C. Both the expression and the final line need checking against the paper.

87₁₀ = 01010111₂ 113₁₀ = 01110001₂

01010111

• 01110001

  11001000₂ Carry: 01110110

11001000₂ = C8₁₆

4.125₁₀ = 100.001₂

Normalised: Mantissa = 0.1000010, Exponent = 0011 (3₁₀)

Mantissa = 0.9375₁₀

Exponent = 7₁₀

Answer = 0.9375 × 2⁷ = 120₁₀

A foreign key is a primary key from one table included in another table, used to form links between tables.

Example: TeacherID in the Courses table, or StudentID/CourseID in a Student-Course link table.

A flat file system may contain a number of single tables with no links between them, whereas a relational database normally contains a number of linked tables (relations).

Entities: Student, Course, Teacher

Teacher —(one-to-many)— Course: One teacher teaches many courses, each course has one teacher.

Student —(many-to-many)— Course: A student can study many courses, and a course can have many students. This requires a link table (Student-Course).

erDiagram
    TEACHER ||--o{ COURSE : teaches
    STUDENT ||--o{ STUDENT_COURSE : enrols
    COURSE ||--o{ STUDENT_COURSE : "is taken in"

Object-oriented programming uses objects and classes which include both data and associated processing.

Encapsulation — the technical implementation is hidden within the object.

Inheritance — properties and methods from a class are copied to another class.

Polymorphism — a form of overloading which allows general object structures to be used with a wider range of data types.

A class defines the methods and properties (data) for a group of similar objects. Once an object is created, knowledge of its implementation is not necessary for its use.

Objects control how other objects interact with themselves, preventing errors. Objects created using OOP can easily be reused in other programs.

Num is Integer Divisor is Integer Prime is Boolean set Prime = TRUE set Divisor = 2 output “type in a number” input Num

repeat if Num MOD Divisor = 0 then set Prime = FALSE end if set Divisor = Divisor + 1 until (Prime = FALSE) OR (Divisor = Num)

if Prime = TRUE then output Num, “is a prime number” else output Num, “is NOT a prime number” end if

Marking: Declare/initialise variables, input number, loop, selection to determine prime, correct terminating condition, output if prime, output if not prime, algorithm works correctly.

A tree-like diagram showing a root directory with subdirectories branching off, and files within those subdirectories. For example: Root → Documents, Programs → Documents/Report.doc, Programs/App.exe

flowchart TD
    R["Root"] --> D["Documents"]
    R --> P["Programs"]
    D --> F1["Report.doc"]
    D --> F2["Notes.txt"]
    P --> F3["App.exe"]

More convenient/easier/faster to find and access files. Allows storing related files in a logical way in the same directory. Can use the same file name in different directories.

Archive — indicates the file is no longer in regular use but may be required sometime in the future.

System — indicates the file is only used by the operating system (e.g. a device driver).

Hidden — the user is unable to see the file (e.g. many files are hidden in Windows as users cannot view or amend them in certain directories).

Bubble sort:

• A number of passes is made until the data is in order.
• For each pass, each value is compared with the following one and swapped if necessary.

Insertion sort:

• Items are copied one by one.
• Each new item is inserted in the correct place in the output.
• Other items are moved along to make room.

The DPA requires organisations to ensure:

• Data must be adequate, relevant and not excessive

• Data must be accurate and up to date

• Personal data stored for no longer than necessary

• Processed in line with your rights — individuals can check and amend data

• Held securely

• Data can only be transferred outside EEA to countries with adequate DPA

• Data is fairly and lawfully processed

• Data is processed for limited purposes

High level languages:

• Easier to understand, learn and program as commands are more English-like
• Identifiers can be long and meaningful
• Allow use of powerful commands that perform complex tasks
• Allow creation of reusable modules

Low level languages:

• Ideal when execution speed is critical (e.g. bootstrap loader)
• More efficient than high level programs
• Require less time for translation into machine code
• Generally result in smaller executable programs

IDE tools:

• Editor — enter and edit source code and annotation
• Compiler — translates source code into machine code
• Interpreter — translates and executes each line of source code
• Automatic formatting — correctly indents code
• Automatic colour coding — changes keywords, literals and annotation to different colours
• Linker — links previously compiled code from software libraries
• Loader — loads compiled code into memory
• Debugger — locates, identifies and rectifies errors
• Syntax error detection — highlights syntax errors before translation
• Trace — displays order of line execution and variable values
• Break point — interrupts on a specific line for variable inspection; allows single-stepping
• Variable watch — displays current value of any variable during execution
• Memory inspector — displays contents of memory sections

MOD checks if the number is divisible by 2 / calculates the remainder of the inputted number.

If the result of modulus is 0 then the number can be divided by 2 and is an even number.

If the modulus is not exactly 0, then the number is not exactly divisible by 2, hence it is an odd number.

Example: if num MOD 2 = 0 Then

Selection outputs “is an even number” if the condition num MOD 2 = 0 is met, otherwise it outputs “is an odd number”.

Example: for i = 1 To numberstocheck

Repetition checks if numbers are even/odd until all numbers have been checked.

Control Unit / Clock — Manages the Fetch/Decode/Execute cycle; fetches each instruction in sequence, decodes and synchronises it by sending control signals to other parts of the computer.

Arithmetic Logic Unit (ALU) — The processing and manipulation of data consisting of arithmetic operations or logical comparisons, allowing a program to take decisions.

Registers (MAR/MDR/CIR etc.) — A small, fast access, temporary storage typically addressed by mechanisms other than main memory.

Buses (Data Bus / Control Bus / Address Bus) — Connects all internal components of a computer, such as CPU and memory, to the motherboard.

Cache memory / Internal Memory (L1, L2) — Can be accessed by a CPU more quickly than regular RAM; used to execute frequently accessed items of code (e.g. loops).

Editor — allows a programmer to enter and edit source code and annotation.

Compiler — translates source code into machine code.

Interpreter — translates each line of source code and executes it.

Automatic formatting — correctly indents code.

Automatic colour coding — changes keywords, literals and annotation to different colours.

Linker — allows previously compiled code from software libraries to be linked together.

Loader — loads previously compiled code into memory.

Debugger — helps locate, identify and rectify errors in a program.

Trace — displays the order in which lines are executed and variable values.

Break point — interrupts on a specific line for variable inspection; allows single-stepping.

Variable watch — displays current value of any variable during execution.

Memory inspector — displays contents of a section of memory.

Simplex — data transmission is possible in one direction only.

Half duplex — data transmission is possible in both directions, but only in one direction at a time.

Full duplex — data transmission is possible in both directions simultaneously.

A data collision occurs when two sets of data are detected on the network simultaneously.

Once detected, a computer waits for a short (random) time then sends again.

A byte is a collection of 8 bits (e.g. 00101010₂).

A word is the total number of bits that can be manipulated as a single unit by the CPU.

2A₁₆ = 00101010₂ BB₁₆ = 10111011₂

00101010

• 10111011

  11100101₂

From the right-hand side, rewrite up to and including the first ‘1’, then change other 1 digits to 0 and 0 digits to 1.

Or: flip the bits and add one.

Example: 00011011 → 11100101

Mantissa = 13/16 or 0.8125₁₀

Exponent = 3₁₀

Answer = 0.8125 × 2³ = 6.5₁₀

Truncation: a number is approximated to whole number/tenth/hundredth etc. nearer to zero (shortened/cut off). Example: 26.8₁₀ truncated to whole number = 26₁₀ Error = -0.8₁₀

Rounding: a number is approximated to the nearest whole number/tenth/hundredth etc. Example: 26.8₁₀ rounded to whole number = 27₁₀ Error = +0.2₁₀

Rounding is more accurate in this case (smaller absolute error).

The physical location of the record is calculated using a hashing algorithm.

This calculation is carried out on data in the key field (or other mandatory data item).

A data collision occurs when two data items are hashed to the same location.

In this case there needs to be an overflow area where the latest data is stored.

When there are many items in the overflow area, access may become slow.

In which case a new hashing algorithm is required and a larger file may be needed.

Declare MyArray[0 to 6] Declare Start is integer Declare End is integer Declare Found is Boolean Declare Mid is integer set Start = 0 set End = 6 set Found = False input SearchValue

repeat set Mid = (Start + End) DIV 2 if SearchValue = MyArray[Mid] then set Found = True Output “SearchValue found at position”, Mid end if if SearchValue > MyArray[Mid] then set Start = Mid + 1 end if if SearchValue < MyArray[Mid] then set End = Mid - 1 end if until (Found = True) OR (End < Start)

if Found = False then Output “SearchValue not found” end if

Marking: Declare array and initialise variables, input SearchValue, loop structure, comparison and output if found, correct terminating condition, correctly discard upper half, correctly discard lower half, output if not found.

A standard module is one which carries out a common/standard task that can be used in many programs.

Example: print function, input validation, maths functions (e.g. square root).

Benefits:

• No need to write again as it has already been written, decreasing development time
• Less likely to have errors because it has already been tested/used
• Likely to be of high quality/efficient as may have been written by experts

A·(A + C) + C·(A + B)

Step 1: A·A + A·C + C·A + C·B [expanding]

Step 2: A + A·C + C·A + C·B [idempotent: A·A = A]

Step 3: A + A·C + C·B [A·C + C·A is one term]

Step 4: A + C·B [absorption: A + A·C = A]

Note: this working only holds if the first term carries a NOT bar that the question text is missing — WJEC draws the bar as a vector line, which text extraction drops. The S16 AS Unit 1 question paper was not available to confirm the intended expression, so the question has been left as extracted and this answer flagged rather than rewritten.

The recorded working contained the step “A·(C + C)” with the aside “C + C combines”, which only makes sense as C + C̄ = 1. That points to the second term being C̄·(A + B), which would give A + B·C̄ rather than A + B·C.

Entities: Department, Course, Module, Student

Department —(one-to-many)— Course: One department offers several courses. Course —(one-to-many)— Module: One course has many modules. Course —(one-to-many)— Student: One course has many students (a student enrols on a particular course).

erDiagram
    DEPARTMENT ||--o{ COURSE : offers
    COURSE ||--o{ MODULE : "made up of"
    COURSE ||--o{ STUDENT : "enrolled on by"

Direct (‘big bang’) changeover:

• Sudden change to new system
• Can be cheaper to implement
• New system is available immediately
• Can be least disruptive if implemented well
• But new system may not work well until staff are trained
• If new system fails, organisation has no system — could be costly or dangerous

Parallel running:

• Both systems run together for a time
• Safest option — if new system fails, old system still available
• Outputs can be compared to verify correctness
• Expensive as requires temporary staff or overtime
• Could cause confusion with two systems

Phased changeover:

• Part-by-part (by functionality)
• Allows gradual adjustment; staff training in stages
• Problems can be fixed one area at a time
• Slower; some systems cannot easily be broken by functionality

Pilot changeover:

• Part-by-part (by part of the organisation)
• All features fully trialled; if something goes wrong, only small part affected
• Pilot staff can help train others
• No backup for the pilot department if things go wrong

Diagrams used in analysis and design.

Descriptions of procedures and subroutines used.

Data structures — what data structures have been used, database table designs.

Algorithm designs — presented in pseudo-code or flowchart form.

Annotated code listings — self-documenting and/or annotated code.

Variable lists — key variables listing data types and purpose.

Data dictionary — describes all fields including data type, size, relationships.

Design documents from the design phase.

Hardware and software requirements (performance, storage, networking, compatibility, OS).

Configuration guide and options.

Backup procedures:

• Generation file backup (grandfather-father-son): stores three most recent versions of master file. If one version is corrupted, previous versions are available. Data should be stored off-site.
• Incremental backup: only backs up changed data, saves storage space and is faster than full backup. Only allows restoring the most recent backup.
• Delta change backup: only data changed since previous backup is stored; original backup is also maintained.

General procedures: test if backups can be restored, frequency of backup, timing (e.g. overnight), designated staff member responsible.

Storage comparison:

• External hard disk drive: very fast transfer, cheap per byte, physically small and portable, can be stored in a fireproof safe.
• Cloud storage: fast transfer (depending on network), data stored securely on protected servers, suitable for large companies with contracts in place.
• Magnetic tape: serial access (can be slow), relatively cheap per unit, physically small, widely used historically by large companies.
• Flash memory stick: very fast, cheap, physically small, but not suitable for large company backups.

Application 1 (e.g. supermarket self-checkout): Barcode scanner — reads product barcodes optically. Advantage: fast and accurate, no manual data entry. Disadvantage: cannot read damaged or obscured barcodes.

Application 2 (e.g. ATM / cash machine): PIN pad / numeric keypad — user presses numeric keys to enter PIN. Advantage: familiar to users and physically secure. Disadvantage: limited to numeric input only.

(Any two different valid applications and appropriate devices accepted. 1 mark: device in context; 1 mark: advantage; 1 mark: disadvantage — per device.)

Advantages (any 2): • Multiple bits transmitted simultaneously across separate wires, so data transfer is faster • Higher effective bandwidth for the same clock speed

Disadvantages (any 2): • Requires more wires / connections, making it more expensive and physically bulkier • Signal skew: bits travelling on different wires arrive at slightly different times, causing synchronisation problems over longer distances • Limited practical distance — crosstalk and interference increase with cable length • More complex and costly connectors/interfaces

A collision is detected on the bus. All transmitting devices stop transmitting and wait for a random period of time before attempting to retransmit. (This is CSMA/CD — Carrier Sense Multiple Access with Collision Detection.)

• Each packet contains a header with a destination IP address (and source address, sequence number, etc.)

• Packets are sent from node to node across the network

• At each router/node, the destination address is read

• The router consults its routing table to find the best next hop (route) toward the destination

• Different packets of the same message may travel by different routes through the network

• Packets arrive at the destination (possibly out of order) and are reassembled in the correct order using sequence numbers

01011.010

• 01101.101

  11000.111

11000.111₂ = 16 + 8 + 0.5 + 0.25 + 0.125 = 24.875₁₀

True value = 24.875

Truncation to 1 d.p.: 24.8 (digits beyond first decimal place are dropped) • Absolute error = |24.875 − 24.8| = 0.075 • Relative error = 0.075 / 24.875 × 100 ≈ 0.301%

Rounding to 1 d.p.: 24.9 (0.875 rounds up to 0.9) • Absolute error = |24.875 − 24.9| = 0.025 • Relative error = 0.025 / 24.875 × 100 ≈ 0.100%

Rounding produces a smaller absolute and relative error.

Step 1: Ā·(1 + C) = Ā·1 = Ā [Identity: 1 + X = 1]

Step 2: Expand (C + B)·(B̄ + C): = C·B̄ + C·C + B·B̄ + B·C = C·B̄ + C + 0 + B·C [C·C = C; B·B̄ = 0] = C·(B̄ + 1 + B) = C·1 = C [B̄ + 1 = 1]

Step 3: C + Ā

MASTER FILE: • Missing field name (Integer, first row): Employee ID — Primary Key (Y) • Example validation: Date of birth — range check (must be a valid past date); or Tax code — format check; or Gross pay to date — range check (must be ≥ 0)

SORTED TRANSACTION FILE: • Missing field name (Integer, first row): Employee ID — Foreign key (links to master file); mark as Primary Key if this identifies each transaction • Example validation: Hours worked — range check (0 to 168 for a weekly payroll); or Gross pay — range check (≥ 0)

(1 mark each: correct master file field name; master file key marked; master file validation; correct transaction file field name; transaction file validation)

Batch processing is the most suitable mode.

• Payroll transactions (hours, pay data) are collected and accumulated over a period (e.g. a week/month)

• All transactions are processed together at one time (e.g. at end of pay period)

• No need for interactive/real-time processing — payslips are only needed periodically

• Processing can be scheduled off-peak (e.g. overnight) for efficiency

• The master file is updated in sequence with the sorted transaction file

• No/reduced data redundancy: each piece of data is stored once in the appropriate table, avoiding duplication across files

• Data consistency: updating one field in one place automatically maintains consistency — no risk of one file being updated while another is not

• Referential integrity: foreign keys enforce valid relationships between tables

• Data relationships: complex many-to-many and one-to-many relationships can be modelled using linked tables

• Powerful querying: SQL allows complex queries joining multiple tables

• Data independence: changes to data structure (e.g. adding a field) do not require changes to all applications

• Multi-user access: different users/applications can access different tables simultaneously with concurrency control

• DBMS features: built-in security, backup and recovery, access control, transaction management

• Scalability: easier to extend the database by adding new tables

• Graphical User Interface (GUI): provides windows, icons, menus, and pointer so users can interact with hardware without needing technical knowledge (e.g. clicking a print icon sends data to printer)

• Command Line Interface (CLI): accepts text commands that are translated into hardware operations

• Device drivers: act as translators between OS/application software and specific hardware devices; each device has its own driver, hiding hardware-specific details from applications

• File management system: provides a logical view of storage (files and folders) rather than raw disk sectors; handles reading/writing to disk hardware transparently

• Memory management: manages RAM allocation and virtual memory (swap space), hiding physical memory details from users and programs

• Process/task management: allows users to launch, switch between and close applications; schedules processes on the CPU

• Hardware abstraction layer (HAL): applications make generic calls to the OS, which translates them into hardware-specific instructions — so the same application runs on different hardware

• I/O management: buffers input/output operations between slow peripheral devices and the faster CPU

Variable: • A named storage location in memory that holds a value • The value stored can change during program execution • Has a data type (e.g. integer, string, Boolean) • Has an identifier (name) used to refer to it in code • Has a scope (the region of the program where it is accessible)

Parameter: • A value that is passed into a subroutine/function/procedure when it is called • Acts as a local variable within the subroutine • Allows data to be communicated to subroutines without using global variables • Can be passed by value (a copy is passed; changes don’t affect the original) or by reference (the memory address is passed; changes affect the original variable)

Scope — the region of code where a variable can be accessed: • Local variable: declared inside a subroutine; only accessible within that subroutine • Global variable: declared at the top level of a program; accessible from anywhere in the program

Lifetime — how long a variable exists in memory: • Local variable: created when the subroutine is called and destroyed when the subroutine returns • Global variable: exists for the entire duration of the program’s execution (from program start to end)

INPUT binaryStr
IF LENGTH(binaryStr) ≠ 8 THEN
    OUTPUT "Error: must be exactly 8 characters"
ELSE
    valid ← TRUE
    FOR i ← 0 TO 7
        IF binaryStr[i] ≠ '0' AND binaryStr[i] ≠ '1' THEN
            valid ← FALSE
        END IF
    END FOR
    IF valid = FALSE THEN
        OUTPUT "Error: must contain only 0s and 1s"
    ELSE
        denary ← 0
        power ← 128
        FOR i ← 0 TO 7
            IF binaryStr[i] = '1' THEN
                denary ← denary + power
            END IF
            power ← power DIV 2
        END FOR
        OUTPUT denary
    END IF
END IF

Alpha testing: • Carried out by the development team / in-house testers (not end users) • Performed at the developer’s site in a controlled environment • Uses both black-box and white-box testing techniques • Goal: find and fix major bugs before release to external users • Testers have knowledge of the system’s internal workings

Beta testing: • Carried out by a selected group of real end users before full public release • Performed in real-world environments on users’ own hardware/software • Users report bugs and usability issues they encounter during normal use • Goal: find bugs missed during alpha testing; test in real-world conditions • Testers generally do not know the internal workings of the system

Key difference: alpha is internal/developer testing; beta is external/user testing in real environments.

• Breakpoints: the programmer sets a breakpoint at a specific line; program execution pauses at that line, allowing the state of variables to be inspected

• Variable watch window: displays the current values of selected variables while execution is paused at a breakpoint

• Single-stepping (step-over / step-into / step-out): executes the program one statement at a time, allowing the programmer to trace the exact path of execution and spot where values become incorrect

• Call stack display: shows the sequence of subroutine calls that led to the current execution point, helping identify where an error was triggered

• Syntax highlighting / error underlining: the IDE flags syntax errors immediately as code is typed, before the program is run

• Integrated debugger: combines all the above tools so the programmer can run, pause, inspect, and step through code without leaving the editor

1. Lexical analysis: • Scans source code and removes whitespace and comments • Converts the source into a stream of tokens (keywords, identifiers, literals, operators) • In this program: FOR, TO, INPUT, OUTPUT identified as keyword tokens; ‘number’, ‘total’, ‘i’ as identifier tokens; 10, 1 as literal tokens • ‘ouptut’ (line 6) is not a recognised keyword — flagged as an unrecognised token / lexical error • ‘grandTotal’ (lines 11–12) is an identifier token (not declared — error caught in semantic analysis)

2. Syntax analysis (parsing): • Checks that the sequence of tokens conforms to the grammar rules of the language • Builds a parse tree / abstract syntax tree (AST) • The misspelled ‘ouptut’ would cause a syntax error as it doesn’t form a valid statement

3. Semantic analysis: • Checks meaning: type checking, undeclared identifiers, uninitialised variables • ‘grandTotal’ (lines 11–12) is used but never declared (only ‘number’ and ‘total’ are declared) → semantic error: undeclared variable • ‘total’ is declared (line 3) but never initialised to 0 before use in line 8 → semantic warning / potential error

4. Code generation: • Translates the validated AST into object code / intermediate code / machine code • Only reached if all previous stages complete without fatal errors • For this program, code generation would not proceed due to errors in earlier stages

5. Optimisation (may occur before or after code generation): • Improves the efficiency of the generated code (e.g. removing redundant instructions, simplifying expressions) • For example, line 11 (grandTotal = total) followed by output could be simplified by outputting total directly

Award 1 mark each, max 2: • Transmitting data where information is sent one bit at a time • Over a single communication channel • Data is transmitted sequentially

Award 1 mark each, max 2: • Transmitting multiple bits of data simultaneously • Over multiple channels/wires • Ideal for short distance high-speed communication

Award 1 mark each, max 2: • USB • Connecting peripherals like keyboards, mice and external storage devices to a computer • Ethernet • Transmitting data between computers over LANs

Award 1 mark each, max 2: • Buses • Transmitting data between the CPU, RAM, and other internal components of a computer • Integrated Circuit (IC) Communication • Communication between components within microprocessors or memory chips

Award 1 mark each, max 4: • Fragmentation is more likely to take place in HDDs • This occurs when files are saved, modified, or deleted over time • Files are stored in available blocks, but as files grow in size, they may not fit into contiguous blocks • Causing the file to be split across multiple locations • Read/write access time increases due to movement of mechanical parts in HDD

Award 1 mark each, max 4: • Defragmentation is the process of reorganising data on a disk to eliminate fragmentation • Analysing the disk to identify fragmented files — the OS or defragmentation tool scans the disk to detect files split into non-contiguous blocks • A report is generated, showing the percentage of fragmentation and which files are scattered across the disk • Begins to move fragmented parts of files to available contiguous spaces on the disk • Copying the fragmented parts of a file and placing them in adjacent sectors, where the entire file can be stored together • Moving files closer together creates larger contiguous blocks of free space • After the files have been rearranged, the file system’s internal pointers are updated to reflect the new locations of the files

Award 1 mark each, max 4: • Occurs when two or more devices on a network attempt to transmit data simultaneously over a shared communication medium • Collisions are more likely to occur on a bus network • In a half-duplex communication channel, when a device is in the process of sending data and another device tries to transmit at the same time, a collision will occur • When multiple devices try to send data on the shared bus at the same time, collisions occur because there is no dedicated path for each device • These collisions corrupt the data, and the packets must be resent • Collisions are more likely to occur in high network traffic • When the number of devices on the network increases, so does the volume of data being transmitted across the network

Award 1 mark for description and 1 mark for collision reduction.

Description: • Data can flow in both directions, but only one direction at a time • Devices take turns sending and receiving data

Collision reduction: • When one device is transmitting, the other must wait until the transmission is complete before it can send data • If two devices attempt to send data simultaneously, collision detection methods are used to manage and resolve collisions

Award 1 mark for description and 1 mark for collision reduction.

Description: • In full-duplex communication, data can flow in both directions simultaneously on the same connection • This method is common in modern switches and network cards

Collision reduction: • Full-duplex communication requires a dedicated communication path for both sending and receiving signals, often using separate physical channels or advanced signalling techniques • Devices don’t need to take turns; they can send and receive data at the same time • Full-duplex eliminates collisions entirely within its communication link because simultaneous bidirectional communication prevents data from clashing on the same path

A + B

A XOR B / A ⊕ B

A̅.B

Award 1 mark for each: • A7 = 10100111 • 49 = 01001001 • Added = 11110000

Award 1 mark for each: • 01101.101 • Mantissa: 0.1101101 • Exponent: 0100

Award 1 mark for each: • Truncation: 37.67 • Rounding: 37.68

Award 1 mark each, max 2: • Floating-point allows the representation of very large and very small numbers • Efficient use of memory • It accurately represents decimal (fractional) values, crucial for scientific and mathematical tasks • Enables straightforward mathematical operations like multiplication and division compared to fixed-point • Designed to tolerate rounding errors, making it suitable for applications requiring approximations

Award 1 mark each, max 4: • They act as specialised software programs that allow the operating system (OS) and applications to interact • They allow communication between the OS and hardware devices such as printers, keyboards, graphics cards, and network adapters • Without device drivers, the operating system would not be able to effectively manage or utilise the hardware • It translates high-level requests into low-level commands that the hardware understands • Device drivers are often hardware-specific, meaning they are written to control a particular type of hardware or model • Device drivers act as mediators between the operating system and the hardware, ensuring smooth communication between the two • They help manage the resources (such as I/O ports, memory addresses, and interrupts) that the hardware requires to function • Device drivers are responsible for handling interrupts and passing them to the OS

Award 1 mark each, max 4: • Antivirus software — protects the system from malware, viruses, and other malicious software that can corrupt or steal data • Firewall software — prevents unauthorised access to the system by monitoring and controlling incoming and outgoing network traffic • Encryption — protects sensitive data by converting it into an unreadable format, making it inaccessible to unauthorised users • Backup and recovery — ensures data integrity and availability by creating copies of important files and recovering them in case of data loss, theft, or corruption • Password management tools — protects user accounts and sensitive data by securely storing and managing passwords

Accept any other valid response.

Award 1 mark for each simplification, max 7: • B.A + B.B̅ + A.B + A.C + A.B + A.C̅ • B.A + 0 + A.B + A.C + A.B + A.C̅ • A.B + A.B + A.C + A.B + A.C̅ • A.B + A.C + A.C̅ • A.B + A.(C + C̅) • A.B + A.(1) • A.B + A • A

Award full marks for correct simplification.

Award 1 mark for appropriate primary key, 1 mark for appropriate field name with data type, 1 mark for appropriate validation.

Indicative content: Car reg | Primary key | String | Format / Presence Make | | String | Presence / Lookup Model | | String | Presence / Lookup Colour | | String | Presence / Lookup Year | | Integer | Range / Length Cost | | Real | Range Mileage | | Integer | Range

Award 1 mark for each, max 6: • Correct Employee with primary key • Correct Sales with primary key • Correct Car with primary key • Correct EmployeeID foreign key • Correct CarID foreign key • Correct one-to-many Employee to Sales relationship • Correct one-to-one Sales to Car relationship

erDiagram
    EMPLOYEE {
        int EmployeeID PK
    }
    SALES {
        int SaleID PK
        int EmployeeID FK
        int CarID FK
    }
    CAR {
        int CarID PK
    }
    EMPLOYEE ||--o{ SALES : makes
    SALES ||--|| CAR : "is for"

Sequences give instructions or operations that are executed ensuring that commands are carried out one after another in a linear fashion.

Making decisions based on conditions, allowing the program to choose different paths or actions depending on the circumstances.

Allows a set of instructions to be executed multiple times until a specified condition is met.

Indicative content:

noOrders is integer totalItems is integer totalBoxes is integer itemsPerBox is integer remainderItems is integer

input “No. of Orders to process:” noOrders

for i = 1 to noOrders

input “Enter No. Items” totalItems input “Enter No. Boxes” totalBoxes if totalItems <= 0 OR totalBoxes <= 0 then output “Enter positive numbers” end if

if totalBoxes > totalItems then output “There are too many boxes” end if

itemsPerBox = totalItems DIV totalBoxes remainderItems = totalItems MOD totalBoxes

if remainderItems > 0 then output “The number of items in each box will be” itemsPerBox output “The remaining items will be” remainderItems else output “The number of items in each box will be” itemsPerBox output “There are no remaining items” end if next i

end

Award 1 mark for each of: • initialise variables • input number of orders, items and boxes • loop • initialising length of loop from input • suitable validation check • correctly determines number of items in a box (DIV or /) • correct use of MOD to calculate remainder • output suitable information on items per box including remainder

Award 1 mark each, max 2: • Evaluate project viability — determine if the proposed system is feasible in terms of technical, financial, and operational aspects • Identify potential challenges — highlight risks, limitations, or constraints that might impact the project • Support decision-making — provide actionable insights to help stakeholders decide whether to proceed • Set scope and objectives — define clear goals and boundaries for the project • Compare alternatives — assess different approaches to find the most effective solution • Predict outcomes — estimate expected benefits, performance, and ROI for the system

Award 1 mark each, max 6: • Preliminary analysis — identify the problem or opportunity and determine if the feasibility study is warranted • Define requirements — gather detailed information about the project’s goals, needs, and constraints • Assess feasibility areas: ◦ Technical feasibility — analyse whether the system can be developed with available technology and expertise ◦ Economic feasibility — examine the cost-effectiveness and financial implications ◦ Operational feasibility — ensure the system aligns with organisational processes and user needs ◦ Legal/regulatory feasibility — confirm compliance with laws and regulations • Analyse alternatives — evaluate different solutions, including their risks and benefits • Document findings — prepare a feasibility report summarising conclusions and recommendations • Present recommendations — share the results with stakeholders to support decision-making

Accept any other suitable response.

Banded response, max 12 marks (Band 3: 9-12, Band 2: 4-8, Band 1: 1-3).

Role of computers in graphics and animation: • Design and creation — essential for creating detailed and complex graphics and animations, from simple logos to intricate 3D models • Rendering — enable the rendering of high-quality images and animations, transforming 2D and 3D models into lifelike visuals • Editing and post-production — facilitate colour correction, special effects, and compositing • Simulation and modelling — used for simulating real-world physics and environments • Interactivity — allow creation of interactive graphics, such as those in video games and virtual reality • AI-generated graphics — AI can generate graphics and images with minimal human input • Collaboration — cloud-based tools enable real-time collaboration among artists across the globe • Customisation — highly customisable workflows and tools tailored to specific project needs

Effects on employment: • Job creation — new roles such as 3D modellers, animators, VFX artists, and game designers • Skill shift — growing demand for technical skills in software like Adobe Creative Suite, Blender, Maya, and AI tools • Remote work — many jobs can be done remotely, offering flexibility but increasing global competition • Automation — some tasks can be automated, potentially reducing the need for certain manual roles • AI impact — AI can automate repetitive tasks, allowing artists to focus on creative aspects, but may reduce demand for entry-level positions • Freelancing — rise of freelancing platforms increases opportunities but introduces job security challenges

General benefits: efficiency, precision, innovation, accessibility, AI assistance, versatility, scalability.

General drawbacks: learning curve, cost, job displacement, health issues (eye strain, RSI), AI limitations, security risks, environmental impact.