Key Vocabulary J277 GSCE Computer Science

Computational thinking

Processes behind formulating and expressing problem solutions.

CPU

Central Processing Unit: "The main part of the computer, consisting of the registers, ALU and control unit."

Fetch-decode-execute cycle

"The complete process of retrieving an instruction from storage, decoding it and carrying it out. Also known as the instruction cycle."

ALU

Arithmetic Logic Unit: "Performs calculations (e.g., x = 2 + 3) and logical comparisons (e.g., IF x > 3) in the CPU."

CU

Control Unit: "Decodes instructions. Sends signals to control how data moves around the CPU."

Cache

"Memory in the processor that provides fast access to frequently used instructions and data."

Register

"Tiny areas of extremely fast memory located in the CPU, normally designed for a specific purpose where data or control information is stored temporarily - e.g., MAR, MDR, etc."

Von Neumann architecture

"Traditional computer architecture that forms the basis of most digital computer systems. Instructions are fetched, decoded and executed one at a time."

MAR

Memory Address Register: "Holds the address of data ready to be used by the memory data register or the address of an instruction passed from the program counter. Step two of the fetch-decode-execute cycle."

MDR

Memory Data Register: "Holds data fetched from or to be written to memory. Step three of the fetch-decode-execute cycle."

Program counter

"Holds the address of the next instruction to be executed. Step one of the fetch-decode-execute cycle."

Accumulator

"Holds the result of calculations."

Clock speed

"Measured in hertz, the clock speed is the frequency at which the internal clock generates pulses. The higher the clock rate, the faster the computer may work. The clock is the electronic unit that synchronises related components by generating pulses at a constant rate."

Cache size

"The larger the cache, the more data that can be stored without having to go back to main memory (RAM) - this has a significant impact on processing speed."

Cores

"Part of a multi-core processor, a single component with two or more independent CPUs that facilitate the fetch-decode-execute cycle."

Embedded system

"A computer built to solve a highly specific problem. Not easy to change. For example, the operating system placed inside a washing machine, microwave or set of traffic lights."

Primary storage

"Comprised of random-access memory (RAM) and read-only memory (ROM). It holds data and instructions that the CPU can access more quickly and easily than from secondary storage devices."

RAM

Random-Access Memory: "Volatile (data is lost when the computer is powered off). Read-and-write. Purpose: Temporary storage of currently executing instructions and data - e.g., applications and the operating system."

ROM

Read-Only Memory: "Non-volatile (data is retained when the computer is powered off). Read-only. Purpose: Stores startup instructions, otherwise known as the bootstrap."

Virtual memory

"Using part of the hard disk as if it were random-access memory. Allows more applications to be open than physical memory can hold."

Secondary storage

"Permanent storage of instructions and data not currently in use by the processor. Stores the operating system, applications and data. Read-and-write and non-volatile."

Optical storage

"CD-R, CD-RW, DVD-R, DVD-RW. Use: Music, films and archive files. Low capacity. Slow access speed. High portability. Prone to scratches. Low cost."

Magnetic storage

"Hard disk drive. Use: Operating system and applications. High capacity. Medium data access speed. Low portability (except for portable drives). Reliable but not durable. Medium cost."

Solid-state storage

"Memory cards and solid-state hard drives (SSD). Use: Digital cameras and smartphones. Medium capacity. High portability. Reliable and durable. No moving parts. Fast data access speed. High cost."

Storage capacity

"The amount of data a storage device can store."

Storage speed

"The read/write access speed of a storage device."

Storage portability

"How easy it is to transport a storage device - e.g., solid-state and optical storage are highly portable, whereas magnetic storage is designed to stay in place."

Storage durability

"How resistant a storage device is to damage and wear. Devices with low durability are likely to fail earlier."

Storage reliability

"A relative measure of confidence that a storage device will function correctly and allow you to write, read, delete and modify data."

Storage cost

"The relative price of a storage device - e.g., per megabyte of data."

Bit

"The smallest unit of storage, represented by either a binary 1 or 0."

Nibble

"Half a byte. Four bits."

Byte

"A collection of eight bits."

Kilobyte

"One kilobyte (KB) is 1000 bytes."

Gigabyte

"One gigabyte (GB) is 1000 megabytes (MB)."

Petabyte

"One petabyte (PB) is 1000 terabytes (TB). "

Binary numbers

"Binary describes a numbering scheme with only two possible values for each digit, 0 and 1. In computing, binary refers to any digital encoding system with exactly two possible states - e.g., in memory, storage, processing and communications, 0 and 1 are sometimes called low and high, respectively."

Overflow

"The generation of a number that is too large to be represented by the device intended to store it."

Binary shifts

"Allows you to easily multiply or divide a base-2 binary number. A left shift multiplies the number by 2, while a right shift divides it by 2."

ASCII

American Standard Code for Information Interchange: "A character set devised for early telecommunication systems but proved to be ideal for computer systems. Uses 7 bits, providing 32 control codes and 96 displayable characters. The eighth bit is often used for error checking."

Unicode

"Standard character set that replaces the use of multiple different character sets. Incorporates characters from almost all global languages. A 16-bit extension of ASCII."

Pixels

"The smallest unit of a digital image or graphic that can be displayed on a digital device. A pixel is represented by a dot or square on a computer display."

Metadata

"A collection of data that describes and provides information about other data."

DNS

Domain Name System: Maintains a directory of domain names and translates them to IP addresses.

Decomposition

Breaking down complex problems into easier parts.

Megabyte

"One megabyte (MB) is 1000 kilobytes (KB)."

Terabyte

"One terabyte (TB) is 1000 gigabytes (GB). "

Denary numbers

"A numerical system of notation that uses 10 as its base. The ten decimal base digits are 0 - 9."

Binary arithmetic

"The process of adding two or more positive 8-bit binary numbers (0 - 255)."

Hexadecimal

"A numerical system of notation that uses 16 rather than 10 as its base. The 16 hex base digits are 0 - 9 and the letters A - F."

Character set

"A set of symbols represented by a computer. These symbols, called characters, can include letters, digits, spaces, punctuation marks and control characters."

Colour depth

"Also known as bit depth."

Resolution

The number of pixels in a display, expressed in terms of the number of pixels on the horizontal and vertical axes.

Image quality

The overall detail of an image, affected by colour depth and resolution.

Image file size

The total size of an image file in storage. Size in bits = Width in pixels Height in pixels Colour depth in bits.

Sample rate

The number of samples taken per second, measured in hertz (Hz).

Sample duration

How many seconds of audio a sound file contains.

Sample bit depth

The number of bits available to store each sample (e.g., 16-bit).

Playback quality

The finished quality of the digital sound file - affected by sample rate and bit depth.

Sound file size

The total size of a sound file in storage. Size in bits = Sampling rate Sample resolution Number of seconds.

Compression

The process of reducing the size of a file.

Lossy compression

A compression method that generally involves a loss of quality where it will be least noticed.

Lossless compression

A compression method that allows a file to be recreated in its original quality.

LAN

Local Area Network: Small geographic area. All hardware is owned by the organization using it.

WAN

Wide Area Network: Large geographic area. Infrastructure is hired from telecommunication companies.

Client-server network

A client makes requests to the server for data and connections.

Peer-to-peer network

All computers are equal and serve their own files to each other.

Wireless access point

Hardware that allows a Wi-Fi-enabled device to connect to a network.

Router

Sends data between networks, needed to connect LAN to WAN.

Switch

Sends data between computers on a LAN.

NIC

Network Interface Card/Controller: Hardware that connects a computer to a network.

Transmission media

Physical media used to transmit data - e.g., twisted copper cable, fibre optic, etc.

The internet

A worldwide collection of interconnected computer networks.

Hosting

Websites stored on dedicated servers rented from a hosting provider.

The cloud

Remote servers that store data to be accessed over the internet.

Web server

A program that uses HTTP to deliver web pages to users.

Client

A device that requests and/or uses services from a remote/connected server.

Network topology

The arrangement of connected devices on a network.

Star topology

Computers connected to a central switch.

Mesh topology

Switches/routers connected so there is more than one route to the destination.

Wired connection

A network that connects hardware via physical cables.

Ethernet

A standard for networking LANs using protocols.

Wireless connection

A network that connects hardware via Wi-Fi.

Wi-Fi

Wireless connection to a network.

Bluetooth

A method of exchanging data wirelessly over short distances.

Encryption

Encoding readable data into unreadable data to protect sensitive communications.

IP address

A unique string of numbers identifying each computer using IP to communicate.

MAC address

Media Access Control Address: A unique identifier for network technologies.

Standards

Rules allowing hardware and software from different manufacturers to interact.

Protocol

A set of rules that allow two devices to communicate.

TCP/IP

Transmission Control Protocol/Internet Protocol: Provides error-free transmission between routers.

HTTP

Hypertext Transfer Protocol: A method of requesting and delivering HTML web pages.

HTTPS

Hypertext Transfer Protocol Secure: Encryption and authentication for requesting and delivering HTML web pages. Used in websites that are sending and/or receiving sensitive data (e.g., passwords, bank details).

FTP

File Transfer Protocol: Used for sending files between computers, usually on a wide area network.

POP

Post Office Protocol: Used by email clients to download email from an email server.

IMAP

Internet Message Access Protocol: Used by mail clients to manage remote mailboxes and retrieve email from a mail server.

SMTP

Simple Mail Transfer Protocol: Sends email to a mail server.

Protocol layering

The concept of protocol rules being built up in layers - the layered protocol stack facilitates the various rules being executed in a defined order.

Malware

A broad term that covers all software written to facilitate loss of data, encryption of data, fraud and identity theft.

Social engineering

Most vulnerabilities are caused by humans - not locking computers, using unsecure passwords, not following company network policy or implementing it poorly, not installing protection software, not being vigilant with suspicious emails/files and not encrypting sensitive data.