IGCSE Computer Science Notes Flashcards

Flashcards from IGCSE Computer Science notes to aid in vocabulary review.

Binary Number System

A number system based on the number 2. It uses only two values, 0 and 1, to represent all values.

Hexadecimal Number System

A number system based on the number 16. It uses sixteen values (0-9 and A-F) to represent all values.

Error Codes

An error message generated by the computer; hexadecimal values refer to the memory location of the error.

HTML (HyperText Markup Language) Colour Codes

Used when writing web pages to represent text colors; all colors are combinations of red, green, and blue, with intensity determined by hexadecimal value.

MAC (Media Access Control) Address

A number which uniquely identifies a device on a network, referring to the Network Interface Card (NIC); can be 48/64 bits, shown as 6 groups of two hexa digits.

Universally Administered MAC address

Set by the manufacturer at the factory; rare for the user to change.

Locally Administered MAC address

Easy to change MAC address.

Internet Protocol (IP) Address

Unique address to each device connected to a network, identifying its location; assigned by the Internet Service Provider.

IPv4

32-bit IP address, denary or hexadecimal, using a decimal point.

IPv6

128-bit IP address, broken down into 16 chunks, hexadecimal.

Static IP Address

IP Address that remains the same each time a device logs onto the internet.

Dynamic IP Address

IP Address that changes each time a device logs onto the internet; assigned by the ISP (Internet Service Provider) using Dynamic Host Configuration Protocol (DHCP).

Denary Number System

A number system based on the number 10, using 0-9 as values.

Overflow

The result of a calculation that produces a value too large for the computer’s allocated word size.

Logical Shifts

Moving the bits to the left or right in a register; bits shifted out are replaced with zeros.

Two’s Complement

A method of representing negative numbers in binary.

Standard ASCII

Character set consists of 7-bit codes, 0-127 values, only supports English.

Extended ASCII

Character set consists of 8-bit codes, 0-255 values, supports Latin languages, includes graphical characters

Unicode

Represents all languages; its character set consists of 16-bit codes and approximately 65000 characters.

Sampling

Converting sound waves via an Analogue to Digital Convertor (ADC).

Bit

The smallest unit of data that a computer can process and store.

Byte

Consists of 8 bits.

Nibble

Consists of 4 bits.

Lossy Data Compression

A compression method that reduces the size of a file by permanently removing data.

Lossless Data Compression

A compression method that reduces the size of a file by temporarily altering the data.

Run-Length Encoding

An algorithm that groups repeating patterns and indexes them; used to compress text and image files; reduces the size of a string of adjacent, identical data

Header (Packet)

The IP address of the sender and receiver, sequence number, and size of the packet.

Payload (Packet)

The actual data in the packets (around 64KiB).

Trailer (Packet)

A packet identification method and an error-checking method (CRC).

Cyclic Redundancy Check (CRC)

The sender adds up all the 1-bits in the payload and stores this as a hex value in the trailer before it is sent. The receiver recalculates the number of 1-bits in the payload and if both values match, there’s no error.

Packet Switching

Each packet follows its own path; routers determine the path based on the number of packets waiting to be processed at each node; packets can reach the destination in a different order to that they were sent.

Serial Data Transmission

Data is sent one bit at a time down a single wire.

Parallel Data Transmission

Data is sent multiple bits at a time down multiple wires.

Simplex

Data is transmitted in a single direction only.

Half-Duplex

Data is transmitted in both directions, but only one direction at a time.

Full-Duplex

Data is transmitted in both directions simultaneously.

Universal Serial Bus (USB)

An industry standard that is used to transmit data.

Parity Check

Adds an additional bit to each byte to create an odd or even sum; the receiving device will check each byte of data for errors.

Checksum

Performs a calculation on the data to create a checksum value; a checksum is calculated and added to the data before transmission. After receiving the data, the two checksums are compared to see if the data entered is correct.

Echocheck

Sends a copy of the transmitted data back to the sender to be compared with the original data sent.

Automatic Repeat Request (ARQ)

Uses acknowledgement and timeout to see if data has arrived correctly after transmission.

Check Digit

A type of error detection method that is used for data entry. A calculation is performed on the data entered to create a value which is compared to see if the data entered is correct

Encryption

A method of securing data for storage or transmission that scrambles it and makes it meaningless.

Symmetric Encryption

A type of encryption that uses the same key to encrypt and decrypt data.

Asymmetric Encryption

A type of encryption that uses two different keys (public and private keys) to encrypt and decrypt data.

CPU (Central Processing Unit)

Used for processing and executing instructions and data that are input into the computer so that the result can be output.

Arithmetic Logic Unit (ALU)

Deals with all arithmetic operations such as addition, subtraction, etc. It also handles logical operations that need to be performed such as “AND”, “OR”, “NOT”, etc.

Control Unit (CU)

Has the job of managing and synchronising data and instructions transfer in the CPU. It does this by sending control signals to other components. Additionally, it also decodes instructions sent to it.

Registers

High-speed memory components in the CPU that temporarily store important information.

Program Counter (PC)

Stores the memory address of the next instruction that will be processed

Memory Address Register (MAR)

Stores the memory address of the instruction/data that is about to be fetched from the RAM

Memory Data Register (MDR)

Stores data or instructions that have just been fetched from the RAM

Current Instruction Register (CIR)

Stores the instruction that is currently being processed or decoded by the CPU

Accumulator (ACC)

Stores any interim values or final values created during arithmetic or logical operations done by the ALU

Buses

Communication systems within the computer that transfer data and instructions between components

Address Bus

Carries the memory address of data/instructions in

Data Bus

Carries actual data/instructions

Control Bus

Carries control signals to and from the CU

Cache

Internal, temporary storage space inside the CPU itself. It stores data and instructions which are used regularly by the CPU

System Clock

Located inside the CPU. Its job is to control the processing speed and time taken to execute instructions, as well as control the time intervals between each task and synchronise the entire FDE cycle

Cores

The components in the computer that run the FDE cycle. Each core can run one cycle, i.e process one instruction, at a time.

Embedded System

A combination of software and hardware that is built into a device, which runs on firmware and performs a dedicated function

Input Devices

Allow data to be entered into the system.

Output Devices

Used to tell user information.

Sensors

Input devices that capture analogue data from their immediate environment at set time intervals.

Primary Storage

Data that is directly accessible by the CPU. Random access memory (RAM) and read-only memory (ROM) are examples of this

Secondary Storage

Contains data that is not directly accessible by the CPU and is not currently required by the CPU. It is non-volatile, which means that the data contained in it is not lost if power is switched off

RAM (Random Access Memory)

It stores data temporarily, making it a volatile method of data storage. It stores the data and instructions that are currently being used by the CPU.

ROM (Read-Only Memory)

It stores data permanently, making it a non-volatile method of data storage. It stores the programs that are required for the computer to boot initially.

Magnetic Storage

Uses magnetised and demagnetised dots to store data.

Optical Storage

Uses circular discs and lasers to store data.

Solid-State Storage

Also known as flash storage. It uses transistors and cells to store data, onto which the data is ‘flashed’. These transistors and cells are arranged on a semiconductor chip.

Virtual Memory

A sectioned-off segment of the hard disk drive, which acts as an extension to the primary memory (RAM). It is required for when the RAM is full but more data transfer needs to take place.

Cloud Storage

Data stored by a third-party remote server instead of in local storage. It is accessible via the internet.

Network Interface Card (NIC)

Hardware component that is required by the computer to access any networks by connecting to the routers. It also contains the MAC address

Media Access Control (MAC) Address

Uniquely identifies each computer on a network, which is provided by the manufacturer when the computer is created

Internet Protocol (IP) Address

Assigned by the internet service provider and it uniquely identifies each computer on a network

Software

A series of instructions written in a programming language that performs a function or a task.

System Software

It provides the services that the computer requires, including operating system and utility software (such as anti-virus)

Application Software

It provides the services that the user requires, and runs on the OS. For example: word processors, databases, spreadsheet applications, and web browsers.

Operating System

Plays many diverse roles in a computer system that includes managing files, handling interrupts, providing a user interface, managing peripherals and drivers, managing memory, managing multitasking, providing a platform for running application providing system security and managing user accounts

Interrupt

A signal that is sent to the CPU asking for its attention. These signals allow the CPU to multitask

High-Level Languages

Use English-style words, which are easier to understand for humans. They need to be converted into low-level language to be understood by computers.

Low-Level Languages

Have two types: assembly language and machine code.

Assembly Language

Uses mnemonics in place of words.

Machine Code

Uses 0s and 1s to represent data in the form of binary numbers. It does not need any conversion.

Translators

Required to convert high-level language or assembly language into machine code, which is the only language which can be understood by the computer.

Assemblers

Translate assembly language into machine code. It translates the entire code at once and produces a file. If it finds any errors, it will create an error report and display it once the entire code is read, without producing a file.

Interpreter

Read the code line-by-line. If it finds an error, it will stop immediately and display it to the user. It will not continue to read the code until the error has been corrected. Otherwise, it runs the code.

Compiler

Read the entire code at once. If it finds any errors, it will compile an error report of all the errors and display it to the user. Otherwise, it will run the code and create an executable file.

Integrated Development Environment (IDE)

An interface where users can write, edit and run programs easily.

Internet

A network of computers joined together through infrastructure such as wires and cables

World Wide Web

The collection of websites and web pages accessed using the internet’s infrastructure.

Uniform Resource Locator (URL)

A text-based address to uniquely identify a web page. It contains three sections: the protocol, the domain name and the web page/file name.

Web Browser

Used mainly for the purpose of rendering hypertext markup language (HTML) and displaying web pages to the user.

Cookie

A small text file that stores information about the user

Session Cookies

Temporarily stored in the primary memory. They are only used as long as the browser is still open. As soon as the browser window is closed, the cookie is deleted.

Persistent Cookies

Permanently stored in secondary storage. They are stored until they are deleted by the user, or until they reach a specific expiration date. They’re retrieved each time the browser window is opened.

Digital Currency

A form of payment that is completely electronic and does not require any tangible currency, such as coins or notes.

Crypto Currencies

A subtype of digital currencies which use a decentralised system known as the blockchain