Cambridge IGCSE Computer Science Second Edition - Chapter Review Flashcards

Vocabulary flashcards for reviewing key terms and concepts from the Cambridge IGCSE Computer Science Second Edition textbook.

Bit

The basic computing element that is either 0 or 1, and is formed from the words Binary digit

Binary number system

A number system based on 2, in which only the digits 0 and 1 are used

Hexadecimal number system

A number system based on the value 16 which uses denary digits 0 to 9 and letters A to F

Error codes

Error messages (in hexadecimal) generated by the computer

Media Access Control (MAC) address

Refers to a number which uniquely identifies a device on a network. The MAC address refers to the network interface card (NIC) which is part of the device.

IP address

Identified either as IPv4 or IPv6; it gives a unique address to each device connected to a network identifying their location

HyperText Mark-up Language (HTML)

Used in the design of web pages and to write, for example, http(s) protocols; in the context of this chapter, colours used in web pages are assigned a hexadecimal code based on red, green and blue colours

Overflow error

The result of carrying out a calculation that produces a value that is too large for the computer’s allocated word size (8-bit, 16-bit, 32-bit, and so on)

Logical shift

An operation that shifts bits to the left or right in a register; any bits shifted out of a register (left or right) are replaced with zeroes

Two’s complement

A method of representing negative numbers in binary; when applied to an 8-bit system, the left-most bit (most significant bit) is given the value –128

ASCII code

A character set for all the characters on a standard keyboard and control codes

Character set

A list of characters that have been defined by computer hardware and software. The character set is necessary so that the computer can understand human characters

Unicode

A character set which represents all the languages of the world (the first 128 characters are the same as ASCII code)

Sampling resolution

The number of bits used to represent sound amplitude in digital sound recording (also known as bit depth)

Bit depth

The number of bits used to represent the smallest unit in a sound file

Colour depth

The number of bits used to represent the colours of a pixel

Sampling rate

The number of sound samples taken per second in digital sound recording

Bitmap image

An image made up of pixels

Pixel

Derived from the term 'picture element' , this is the smallest element used to make up an image on a display

Image resolution

The number of pixels in the X–Y direction of an image

Pixelated (image)

This is the result of zooming into a bitmap image; on zooming out the pixel density can be diminished to such a degree that the actual pixels themselves can be seen

Pixel density

Number of pixels per square inch

Compression

Reduction of the size of a file by removing repeated or redundant pieces of data; this can be lossy or lossless

Bandwidth

The maximum rate of transfer of data across a network

Lossy

A file compression method in which parts of the original file cannot be recovered

Lossless

A file compression method that allows the original file to be fully restored during the decompression process

Audio compression

A method used to reduce the size of a sound file using perceptual music shaping

MP3

A lossy file compression method used for music files

MP4

A lossy file compression method used for multimedia files

JPEG

From Joint Photographic Expert Group; a form of lossy file compression used with image files which relies on the inability of the human eye to distinguish certain colour changes and hues

Run length encoding (RLE)

A lossless file compression technique used to reduce the size of text and photo files in particular

Data packet

A small part of a message/data that is transmitted over a network; after transmission all the data packets are reassembled to form the original message/data

Packet header

The part of the data packet that contains the IP addresses of the sender and receiver, and includes the packet number which allows reassembly of the data packets

Packet trailer

The part of a data packet that indicates the end of the data packet and cyclic redundancy check error check

Cyclic redundancy check (CRC)

An error checking method in which all the 1-bits in the data packet payload are added and the total is stored in the packet trailer; the same calculation is repeated at the receiving station

Payload

The actual data being carried in a data packet

Node

Stages in a network that can receive and transmit data packets

Packet switching

A method of transmission in which a message is broken into many data packets which can then be sent along pathways independently of each other

Router

A device that enables data packets to be moved between different networks, for example to join a LAN to a WAN

Real time streaming

The transmission of data over a network for live events where the data is sent as soon as it is received or generated

Hopping/hop number

A number in a data packet header used to stop data packets that never reach their destination from ‘clogging up’ the data paths/routes

Simplex

Data that can be sent on one direction only

Half-duplex

Data that can be sent in both directions but not at the same time

Full-duplex

Data that can be sent in both directions at the same time (simultaneously)

Serial data transmission

Sending data down one channel/wire one bit at a time

Parallel data transmission

Sending data down several channels/wires several bits at a time (usually 1 byte)

Skewed (data)

Data that arrives at the destination with the bits no longer synchronised

Universal serial bus (USB)

A type of serial data transmission which has become the industry standard for connecting computers to devices via a USB port

Parity check

A method used to check if data has been transferred correctly; it makes use of even parity (an even number of 1-bits) or odd parity (an odd number of 1-bits)

Parity bit

A bit (either 0 or 1) added to a byte of data in the most significant bit position; this ensures that the byte follows the correct even parity or odd parity protocol

Parity block

A horizontal and vertical parity check on a block of data being transmitted

Parity byte

An extra byte of data sent at the end of a parity block; it is composed of the parity bits generated from a vertical parity check of the data block

Checksum

A verification method used to check if data transferred has been altered or corrupted; calculated from the block of data of data being sent; the checksum value is sent after each data block

Echo check

A method used to check if data has been transferred correctly; data is sent to a receiver and then immediately sent back to the sender; the sender then checks if the received data matches the sent data

Check digit

An additional digit appended to a number to check if the entered number is error-free; check digit is a data entry check and not a data transmission check

Eavesdropper

Another name for a hacker who intercepts data being transmitted on a wired or wireless network

Encryption

The process of making data meaningless using encryption keys; without the correct decryption key the data cannot be decoded (unscrambled)

Plaintext

The original text/message before it is put through an encryption algorithm

Ciphertext

Encrypted data that is the result of putting a plaintext message through an encryption algorithm

Encryption algorithm

A complex piece of software that takes plaintext and generates an encrypted string known as ciphertext

Symmetric encryption

A type of encryption in which the same encryption key is used both to encrypt and decrypt a message

Asymmetric encryption

A type of encryption that uses public keys and private keys to ensure data is secure

Public key

A type of encryption key that is known to all users

Private key

A type of encryption key which is known only to the single computer/user

Quantum computer

A computer that can perform very fast calculations

Central processing unit (CPU)

Responsible for the execution or processing of all the instructions and data in a computer

Integrated circuit

Typically, a chip made from a semi-conductor material which carries out the same tasks as a larger circuit made from individual components

Von Neumann architecture

A type of computer architecture which introduced the concept of the stored program in the 1940s

Arithmetic & Logic Unit (ALU)

The component of the CPU that carries out all arithmetic and logical operations

Memory address register (MAR)

A register that stores the address of the memory location currently being read from or written to

Current instruction register (CIR)

A register that stores the current instruction being decoded and executed

Memory data register (MDR)

A register that stores data that has just been read from memory or data that is about to be written to memory

Program counter (PC)

A register that stores the address where the next instruction to be read can be found

Control unit

The component of a computer’s CPU that ensures synchronisation of data flow and programs throughout the computer by sending out control signals along the control bus

System clock

Produces timing signals on the control bus to ensure synchronisation takes place

Clock cycle

The vibrational frequency of the system clock which sends out pulses along the control bus

Immediate access store (IAS)

Memory that holds all data and programs needed to be accessed by the control unit

Backing store

A secondary storage device (such as HDD or SSD) used to store data permanently even when the computer is powered down

Cache

Is temporary memory using static RAM to hold frequently used data/instructions by the CPU thereby increasing CPU performance

Register

A temporary component in the CPU which can be general or specific in its use; it holds data or instructions as part of the Fetch–Decode–Execute cycle

Address

A container for a specific memory location used by the CPU to track data

Memory location

A numbered place in memory where values can be stored

System buses

The connection betweem major components in a computer that can carry data, addresses and control signals

Address bus

The system bus that carries the addresses throughout the computer system

Data bus

The system bus that allows data to be carried from CPU to memory (and vice versa) or to and from input/ output devices

Control bus

The system bus that carries signals from control unit to all other computer components

Unidirectional

Describes activity that can travel in one direction only

Bidirectional

Describes activity that can travel in both directions

Word

A group of bits used by a computer to represent a single unit

Overclocking

Changing the clock speed of a system clock to a value higher than the factory/recommended setting

Core

A unit on a CPU made up of an ALU, control unit and registers; a CPU may contain a number of cores

Dual core

A CPU containing two cores

Quad core

A CPU containing four cores

Fetch–Decode–Execute

A cycle by which instructions and data are fetched from memory, decoded and finally executed

Basic Input/Output System (BIOS)

A suite of programs on firmware that are used to perform the initialisation of a computer system during the boot-up process

Opcode

Part of a machine code instruction that identifies what action the CPU has to perform

Operand

Part of a machine code instruction that identifies what data is to be used

Instruction set

The complete set of machine code instructions used a particular microprocessor

Embedded system

A combination of hardware and software designed to carry out a specific set of functions

ASCII code

A barcode that can represent all the characters on a standard keyboard and control codes