Computer Science IGCSE Unit 3

This flashcard set is directly taken from Hodder Education's Cambridge IGCSE and O Levels Computer Science textbook (2nd Edition). This is carefully catered towards the syllabus and understanding of the terms will most likely translate to an understanding of the syllabus to better prepare you for the exams!

central processing unit (CPU)

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

integrated circuit

usually a chip made from a semiconductor 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

accumulator (ACC)

temporary general-purpose register that stores numerical values at any part of a given operation

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

clock speeds are measured in terms of GHz; this is the vibrational frequency of the system clock which sends out pulses along the control bus; for example, a 3.5 GHz clock cycle means 3.5 billion clock cycles a second

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

temporary memory using static RAM to hold frequently used data/instructions by the CPU thereby increasing CPU performance. More generally, cache means any area of storage used to quickly access frequently-used data - other examples include web cache, database cache, DNS cache

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 label for a memory location used by the CPU to track data

memory location

a numbered place in memory where values can be stored

system buses

a connection between major components in a computer that can carry data, addresses or 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

can travel in one direction only; used to describe data

bidirectional

can travel in both directions; used to describe data

word

a group of bits used by a computer to represent a single unit; for example, modern computers often use 64-bit word lengths

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-Execute-Decode

a cycle in 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 by a particular microprocessor

embedded system

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

barcode

a series of dark and light lines of varying thickness used to represent data; the code has to be scanned using laser or LED light source

key field

the field that uniquely identifies a record in a file
quick response (QR) code!a matrix of dark and light squares which represent data; the pattern can be read and interpreted using a smartphone camera and QR app

frame QR code

a type of QR code that includes a space for advertising

DAC (digital to analogue converter)

device that converts digital data into electric currents that can drive motors, actuators and relays, for example

ADC (analogue to digital converter)

a device that converts analogue data (for example, data read from sensors) into a form understood by a computer

charge couple device (CCD)

a light sensitive cell made up of millions of tiny sensors acting as photodiodes

virtual keyboard

an onscreen keyboard which uses the features of the touch screen to emulate a physical keyboard

touch screen

a screen that allows the user to select or manipulate a screen image using the touch of a finger or stylus; touch screens most frequently use capacitive, infra-red or resistive technology

repetitive strain injury (RSI)

pain felt in the muscles, nerves and tendons caused by a repetitive action (for example, excessive clicking of a mouse button over a period of time)

optical mouse

a pointing device that uses a red LED to track the movement of the device and then relays its coordinates to a computer

pointing device

an input device that allows the user to control the movement of an onscreen cursor or to allow onscreen selection by clicking a button on the device

complementary metal oxide semi-conductor (CMOS)

a chip that generates an electric current (or pulses) when light falls on its surface

digital signal processor (DSP)

a processor that calculates, for example, the coordinates of a pointing device based on the pulses of electricity received

optical character recognition

technology that can convert hard copy text or images into a digital format to be stored in a computer memory

computer aided design (CAD)

software used to create drawings (for example, to send to a 3D printer or to produce blueprints of a microprocessor design)

computed tomographic (CT) scanner

technology that can create a 3D image of a solid object by slicing up the object into thin layers (tomography)

capacitive touch screen

a type of touch screen that uses the change in the screen's capacitance (the ability to store an electrical charge) when it is touched by a finger or stylus

infra-red touch screen

a type of touch screen that uses infra-red beams and sensors to detect where the screen has been touched

resistive touch screen

a type of touch screen that uses two conductive layers which make contact where the screen has been touched

actuator

an output device that converts electrical energy into mechanical movement

digital micromirror device (DMD)

a chip that uses millions of tiny mirrors on its surface to create a video display

thermal bubble

inkjet printer technology whereby tiny resistors create heat and form an ink bubble which is ejected onto paper in an inkjet printer

piezoelectric crystal

a crystal located in an ink reservoir within an inkjet printer; the crystal vibrates and forces ink out onto paper

direct 3D printing

a 3D printing technique in which the print head moves in the x, y and z directions

binder 3D printing

a 3D printing method that uses a two-stage pass; the first stage uses dry powder and the second stage uses a binding agent

cathode

a negative electrode

anode

a positive electrode

organic LED (OLED)

a light-emitting diode that uses the movement of electrons between a cathode and an anode to produce an on-screen image; it generates its own light so no backlighting is required

loudspeaker

an output device that converts electric current into sound

memory

the devices within the computer that are directly accessible by the CPU; there are two types of memory - RAM and ROM; memory is different from hard disk drives, for example, which are known as storage devices

random access memory (RAM)

primary memory that can be written to or read from

read only memory (ROM)

primary memory that cannot be written to (changed) and can only be read

dynamic RAM (DRAM)

a type of RAM chip that needs to be constantly refreshed

static RAM (SRAM)

a type of RAM chip that uses flip flops and doesn't need to be constantly refreshed

volatile

describes memory that loses its contents when the power is turned off

refresh

recharge every few seconds in order to maintain charge; for example with a device such as a capacitor

flip flop

electronic circuit with only two stable conditions

latency

the lag in a system; for example, the time it takes to find a track on a hard disk, which depends on the time it takes for the disk to rotate around to its read/write head

SSD endurance

the total guaranteed number of times data can be written to or read from a solid state drive (SSD) in its usable life cycle

optical storage

a type of storage that uses laser light to read and write data, and includes CDs, DVDs, and Blu-ray discs

dual layering

using two recording layers in storage media such as DVDs and some Blu-rays

virtual memory

a memory management system that makes use of secondary storage and software to enable a computer to compensate for the shortage of actual physical RAM memory

disk thrashing (HDD)

a problem in a hard disk drive (HDD) caused by excessive swapping in and out of data causing a high rate of head movements during virtual memory operations

thrash point

the point at which the execution of a program comes to a halt because the system is so busy moving data in and out of memory rather than actually executing the program

data redundancy

the unnecessary storing of the same data on several storage devices at the same time

cloud storage

a method of data storage where data is stored on offsite servers; the physical storage may be on hundreds of servers in many locations

network interface card (NIC)

a hardware component (circuit board or chip) that is required to allow a device to connect to a network, such as the internet

router

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

static IP address

an IP address that doesn't change

MAC address

a unique identifier which acts as a network address for a device; it takes the form NN-NN-NN-DD-DD-DD, where NN is the manufacturer code and DD is the device code

dynamic IP address

a temporary IP address assigned to a device each time it logs onto a network

dynamic host configuration protocol (DHCP)

a server that automatically provides and assigns an IP address