Computer Science - 1.1 (quick)

System Architecture

CPU

Fetches and executes instructions/data

ALU

Carries out math and logic comparisons, there can be multiple in one CPU and is split into; the Logic Unit, and the Arithmetic Unit. Holds the Accumulator.

CU

Directs the operations from the processor. Contains the PC MAR and the MDR.

Cache

Located Around or inside the CPU the Cache is super fast memory close to the CPU to speed up the Fetch and Execute Cycle

PC

Stores the memory address of the next instruction. Is incremented by one after an instruction is fetched.

MAR

Holds memory addresses before they are sent down the address bus. The addresses can either be the locations of instructions, the locations of data or the location to store data.

MDR

Stores either an instruction or data once it is fetched from memory. It receives instructions or data via the data bus. It can also store data before it is send back along the data bus to be stored (the data bus is two way)

Accumulator

Stores a running total of the calculation that is currently happening.

Pipelining

Allows multiple operations to be executed and fetched at once instead of one waiting for the other to come back. This speeds up the Clock Speed

Clock Speed

This is the measure of how many fetch / execute cycles happen every second. This is measured in Hz. One Hz is one fetch / execute cycle per second.

Number of cores

In recent times dual core and quad core CPUs have been invented. This means that inside the CPU there are two or four separate processors.

Cache Size

Sometimes it can be a pain for the CPU to constantly be fetching the same instruction over and over again from memory. If this happens it makes sense to store this repeated instruction close by so it can be retrieved quicker.

RAM

A fast temporary type of memory in which programs, applications and data are stored.