Processor Fundamentals

Key terms to remember

Arithmetic Logic Unit

component in the processor which carries out all arithmetic and logical operations.

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.

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.

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.

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

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.

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.