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3. Hardware
Computer Science CIE IGCSE
| Term | Definition |
|---|---|
| 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 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. |
| 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/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 (CU) | 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. |
| 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. |
| 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. (e.g. 64 bit) |
| 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, CU, and Registers. |
| Dual core | A CPU containing 2 cores |
| Quad core | A CPU containing 4 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 | Apart of a machine code instruction that identifies what data is to be used. |
| Instruction set | The complete set of machine code instructions using 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 on 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 (e.g. 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 of a stylus; use capacitive, infrared, or resistive technology. |
| Repetitive strain injury (RSI) | Pain felt in the muscles, nerves, and tendons caused by a repetative action (e.g. excessive clicking of a mouse or button over a long 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 recieved. |
| Optical character recognition (OCR) | 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 electric charge) when it is touched by a finger or stylus. |
| Infrared touch screen | A type of touch screen that uses infrared 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 the 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 2 types - RAM and ROM. Memory is different to HDDs, for example, which are known as storage devices. |
| Random access memory (RAM | Primary memory that can be written to or read from |
| Dynamic RAM (DRAM) | A type of RAM chip that needs to be constantly refreshed. |
| Read only memory (ROM) | Primary memory that cannot be written to, and can only be read. |
| 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 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 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 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. |
| Dynamic iP address | A temporary IP address assigned to a device each time it logs onto a network. |
| 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 jost configuration protocol (DHCP) | A server that automatically provides and assigns an IP address. |
Created by:
Ginny Martin
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