GCSE OCR Computer Science – Master Revision Flashcards

A comprehensive set of question-and-answer flashcards summarising the key GCSE Computing concepts.

What is the primary purpose of the CPU?

To carry out the processing of data by repeatedly performing the fetch-decode-execute cycle.

Which three key characteristics affect CPU performance?

Clock speed, cache size, and number of cores.

What does the clock speed of a CPU measure?

The number of fetch-decode-execute cycles it can perform per second, measured in hertz (Hz).

Why does a larger CPU cache usually improve performance?

Because recently/frequently used instructions are stored closer to the CPU, reducing fetch time.

What is a CPU core?

An independent processor within the CPU that can execute instructions; multiple cores allow multitasking.

In Von Neumann architecture, where are data and instructions stored?

In the same main memory.

Name the four main CPU registers used in the F-D-E cycle.

Program Counter (PC), Memory Address Register (MAR), Memory Data Register (MDR), Current Instruction Register (CIR).

Give the steps of the fetch phase in the F-D-E cycle.

Copy PC to MAR, fetch instruction into MDR, copy MDR to CIR, increment PC.

Define an embedded system.

A computer system with a processor built into another device, designed for a dedicated task.

Give two examples of embedded systems.

Dishwasher, microwave (others: fridge, smartphone, TV).

State two differences between RAM and ROM.

RAM is volatile and can be changed; ROM is non-volatile and normally cannot be changed.

What is virtual memory?

A section of the hard drive used as an extension to RAM when RAM is full.

Why is flash memory useful in portable devices?

It is non-volatile, has no moving parts (fast, durable), and can be electrically re-written.

What is secondary storage used for?

Long-term, non-volatile storage of files and programs when not in use.

List the three main categories of secondary storage.

Optical, magnetic, solid-state (flash).

Give one advantage and one disadvantage of optical storage.

Advantage: cheap and portable; disadvantage: slow access speeds and can be damaged easily.

Why are HDDs (magnetic) still popular for backups?

They offer very high capacity at low cost, though access is slower than SSDs.

State two advantages of solid-state drives over hard disk drives.

Much faster access speeds and no moving parts (more durable).

Define a computer network.

Two or more computers connected together to share data, resources, or communication.

Differentiate between a LAN and a WAN.

LAN covers a small geographic area with hardware owned by one organisation; WAN covers large areas and uses third-party infrastructure.

What role does a Network Interface Card (NIC) play?

It allows a device to connect to a network and communicates using a unique MAC address.

Why is a switch preferred to a hub in a LAN?

Because a switch sends data only to the intended destination device, reducing collisions.

Name three common wired transmission media.

Twisted-pair (Cat5e/Cat6), coaxial cable, and fibre-optic cable.

Describe a client-server network.

Clients request services/resources from a central, powerful server which also manages security, backups, and software.

Give one advantage of a peer-to-peer network.

Cheap and easy to set up for small/home networks because no dedicated server is required.

State two factors that can slow network performance.

Limited bandwidth with too many users, or wireless interference (also: outdated hardware, topology choice).

How do the Internet and the World Wide Web differ?

The Internet is the global network infrastructure; the WWW is a collection of websites hosted on it.

Give one advantage and one disadvantage of using cloud storage.

Advantage: access files anywhere; disadvantage: requires internet connection and trust in third-party security.

What is the purpose of DNS?

To translate human-friendly URLs/domain names into IP addresses computers use to locate servers.

Define a virtual network.

A software-defined network that exists on top of physical infrastructure, allowing separate logical networks with their own security.

Which two frequency bands are commonly used by Wi-Fi?

2.4 GHz and 5 GHz.

Why does changing Wi-Fi channel sometimes improve performance?

To reduce interference when multiple devices are using overlapping channels.

Explain encryption in networking.

Converting data into a coded form so that it is unreadable without a decryption key.

How does symmetric encryption differ from asymmetric (public-key) encryption?

Symmetric uses the same key to encrypt/decrypt; asymmetric uses a public key to encrypt and a private key to decrypt.

Describe a star network topology.

All devices connect to a central switch or server; failure of that central device brings down the network.

What is a mesh topology’s main advantage?

Multiple routes between devices provide high redundancy and can reduce collisions.

Outline the basic idea of packet switching.

Data is split into equal-sized packets that find independent routes across a network and are reassembled at the destination.

Name three items in a packet header.

Destination IP address, packet number/sequence, and error-checking code (checksum).

What is the main function of TCP compared to IP?

TCP splits data into packets, ensures delivery, and reassembles them; IP handles addressing and routing of packets between networks.

Which protocol securely transfers hypertext over the Internet?

HTTPS (HTTP Secure).

What does SMTP stand for and do?

Simple Mail Transfer Protocol; it sends emails between servers.

Give two benefits of organising network protocols into four layers.

Modularity (each layer can change without affecting others) and interoperability (standardised interfaces enable compatible hardware/software).

Define malware.

Malicious software such as viruses, trojans, or spyware designed to damage or gain unauthorised access to systems.

What is phishing?

Fraudulent emails or messages that trick users into revealing personal information like passwords or bank details.

Describe a brute-force attack.

An attack that systematically tries every possible password combination to gain access.

What is a denial-of-service (DoS) attack?

Flooding a network or web server with excessive traffic to make it unavailable to legitimate users.

Explain SQL injection.

Inserting malicious SQL code into input fields to gain unauthorised access, modify, or delete database data.

What is the purpose of a network policy?

To define rules and procedures that users must follow to keep the network secure and efficient.

Describe penetration testing.

Simulating attacks on a system to discover and fix security vulnerabilities.

How does a firewall protect a network?

By monitoring and filtering incoming and outgoing traffic based on predetermined security rules.

What are user access levels?

Permissions that restrict users to only the data and resources necessary for their role.

List three characteristics of a strong password.

At least 6–8 characters long, mix of upper/lowercase letters, numbers, and symbols; not easily guessable.

Define an operating system.

System software that manages hardware, provides a user interface, and offers common services for applications.

Give three key functions of an OS.

User interface, memory management/multitasking, peripheral (device) management.

What does a device driver do?

Translates OS commands into signals that a specific hardware device understands.

State two tasks performed by file management within an OS.

Organising files in a hierarchy and handling saving, retrieval, and permissions.

What is the purpose of defragmentation software?

To reorganise fragmented files on a hard disk so data blocks are contiguous, improving access speed.

Differentiate between full and incremental backup.

Full copies every file; incremental copies only files changed since the last backup, saving time and space.

Give one advantage and one disadvantage of proprietary software.

Advantage: official support and regular updates; disadvantage: licensing costs and limited customisation.

Why might a developer choose an open-source licence?

To allow community improvement, reach a wider audience, and potentially earn from donations/ads while retaining credit.

What law protects personal data stored by organisations in the UK?

The Data Protection Act (1998).

Which act makes unauthorised access to computer material illegal?

The Computer Misuse Act (1990).

What law protects creative works like software code?

Copyright, Designs and Patents Act (1988).

How does a linear search work?

It checks each item in order until the target is found or the end of the list is reached.

Why is a binary search usually faster than a linear search?

Because it repeatedly halves a sorted list, reducing the number of comparisons needed.

Outline the bubble sort algorithm.

Repeatedly compare adjacent items and swap if out of order; continue passes until no swaps are needed.

What is the main advantage of a merge sort over bubble sort?

Much faster on large lists due to its divide-and-conquer approach (O(n log n) vs O(n²)).

Define a variable and a constant.

Variable: named memory location whose value can change; constant: named location whose value remains fixed during program execution.

Name the three basic programming constructs.

Sequence, selection, and iteration (loops).

Give two common data types and an example of each.

Integer (e.g., 42) and string (e.g., "Hello").

What does the MOD operator return?

The remainder after integer division.

Write pseudocode to read a name and display it.

name ← INPUT("What is your name?") OUTPUT("Your name is " + name)‏

How is the length of a string obtained in pseudocode?

stringName.length

What is an array?

A data structure that stores multiple items of the same data type under one identifier using indices.

Differentiate between a function and a procedure.

A function returns a value; a procedure performs actions but returns no value.

Write an SQL query to select all records from a table called Products.

SELECT * FROM Products;‏

Give two common input validation checks.

Range check and presence check (others: length, format, lookup, check digit).

What is authentication in defensive design?

Verifying the identity of a user, e.g., via username/password or multi-factor methods.

How do indentation and comments aid maintainability?

They make code easier to read, understand, and modify by grouping logic and explaining purpose.

Distinguish between a syntax error and a logic error.

Syntax error violates language rules and prevents running; logic error lets the program run but with incorrect results.

What is ‘valid extreme’ test data?

A value at the upper or lower boundary that should be accepted by the program.

What does an AND logic gate output when both inputs are 1?

1 (true).

Convert the 8-bit binary 01010101 to denary.

85.

Add binary 00001111 and 00000001.

00010000 (with no overflow).

Why is hexadecimal often used by programmers?

It is shorter and easier to read than binary and converts neatly (4 bits per hex digit).

What effect does a left binary shift of one place have?

Multiplies the binary number by 2.

Define pixel, colour depth, and resolution.

Pixel: smallest picture element; colour depth: bits per pixel determining colour range; resolution: number of pixels per unit area (e.g., DPI).

State two factors that increase sound file size and quality.

Higher sampling frequency and larger bit rate (bits per sample).

Differentiate between lossy and lossless compression.

Lossy removes data permanently for smaller files (quality loss); lossless compresses without data loss but with less size reduction.

What does an assembler do?

Translates assembly language source code into machine code.

Give one advantage of a compiler over an interpreter.

Compiled object code runs faster and can be distributed without source code.

Name two common tools found in an IDE.

Code editor with syntax highlighting and error diagnostics (others: run-time environment, translator).