Control unit – 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. Immediate access store (IAS) – holds all data and programs needed to be accessed by the control unit. Accumulator – temporary general purpose register which stores numerical values at any part of a given operation. Register – temporary component in the processor which can be general or specific in its use that holds data or instructions as part of the fetch- execute cycle. Status register – used when an instruction requires some form of arithmetic or logical processing. Flag – indicates the status of a bit in the status register, for example, N = 1 indicates the result of an addition gives a negative value. Address bus – carries the addresses throughout the computer system. Data bus – allows data to be carried from processor to memory (and vice versa) or to and from input/output devices. Control bus – carries signals from control unit to all other computer components. Unidirectional – used to describe a bus in which bits can travel in one direction only. Bidirectional – used to describe a bus in which bits can travel in both directions. Word – group of bits used by a computer to represent a single unit. Clock cycle – clock speeds are measured in terms of GHz; this is the vibrational frequency of the clock which sends out pulses along the control bus – a 3.5 GHZ clock cycle means 3.5 billion clock cycles a second. Overclocking – changing the clock speed of a system clock to a value higher than the factory/recommended setting. BIOS – basic input/output system. Cache memory – a high speed auxiliary memory which permits high speed data transfer and retrieval. Core – a unit made up of ALU, control unit and registers which is part of a CPU. A CPU may contain a number of cores. Dual core – a CPU containing two cores. Quad core – a CPU containing four cores. Port – external connection to a computer which allows it to communicate with various peripheral devices. A number of different port technologies exist. Universal Serial Bus (USB) – a type of port connecting devices to a computer. Asynchronous serial data transmission – serial refers to a single wire being used to transmit bits of data one after the other. Asynchronous refers to a sender using its own clock/timer device rather sharing the same clock/timer with the recipient device. High-definition multimedia interface (HDMI) – type of port connecting devices to a computer. Video Graphics Array (VGA) – type of port connecting devices to a computer. High-bandwidth digital copy protection (HDCP) – part of HDMI technology which reduces risk of piracy of software and multimedia. Fetch-execute cycle – a cycle in which instructions and data are fetched from memory and then decoded and finally executed. Program counter (PC) – a register used in a computer to store the address of the instruction which is currently being executed. Current instruction register – a register used to contain the instruction which is currently being executed or decoded. Register Transfer Notation (RTN) – short hand notation to show movement of data and instructions in a processor, can be used to represent the operation of the fetch-execute cycle. Interrupt – signal sent from a device or software to a processor requesting its attention; the processor suspends all operations until the interrupt has been serviced. Interrupt priority – all interrupts are given a priority so that the processor knows which need to be serviced first and which interrupts are to be dealt with quickly. Interrupt service routine (ISR) or interrupt handler – software which handles interrupt requests (such as ‘printer out of paper’) and sends the request to the CPU for processing.