A Level Computer Science Paper 1: 1.1.1 Processors, Input, Output and Storage

A computer can process an input from a user in order to reach an output

Central processing unit

What it is being used for

e.g. phone is smaller than a PC and is battery powered without a fan so it needs a smaller CPU with less functions

Control Unit
Buses
Arithmetic Logic Unit
Designated Registers

Processes instructions for the CPU

Move signals around
Consist of connectors that transfer signals between components
8/16/32/64 lines

Address bus - where it is going ; CPU to RAM
Data bus - carries the data around ; both ways
Control bus - controls data instructions ; both ways

Carries out arithmetic and outputs - stores results in the accumulator

Current instruction register

Holds the current instruction that is being followed

Program counter

Memory address of the next instruction

Memory address register

Holds the address of where data is being read/written

Memory data register

Holds data between processor and memory

Accumulator

Stores the result of logical calculations

Their full names - NO ACRONYMS

CPU fetches data and stores in registers

1. PC transfers address of next instruction to MAR

2. Instruction from that address is carried to MDR

3. Simultaneously PC value increases by 1

4. Contents of MDR are transferred to CIR

5. Instruction held in CIR is decoded

6. Split into operand and opcode to define the type of instruction and acquire any additional data

7. Passed to ALU

8. Instruction is executed and result stored in accumulator or memory

opcode has the instruction

operand has the data and address.

The equal units memory is divided into, usually 8/16/32/64 bits
Each has a separate memory address

The width determines the maximum possible memory addresses (2 to the power of width addresses)

8 bits opcode - 6 instruction, 2 clarify what

8 bits operand

Clock speed
Number of core
Cache memory
Buses

It increases the speed of the fetch/decode/execute cycle.
The faster clock speed the more instructions executed per second.
You can overclock if the clock speed is too high

They can process more instructions simultaneously

Parallel processing - where multiple cores work on different elements of the same task to complete it quicker

They can process more instructions simultaneously

Parallel processing - where multiple cores work on different elements of the same task to complete it quicker

A small amount of superfast memory that stores recent data and instructions
Level 1 cache smaller but faster, cores share level 2
More allows for better performance

A bigger address bus allows you to have more address locations, storing more data and instructions

Changing CPU for clock speed/ more cores/ more cache
More or faster RAM
Change graphics card
SSD (Solid state drive)

Overlapping stages of the F/D/E cycle to improve performance
One line is executed as the next is decided and the one after that fetched
Data is held in a buffer

Conditionals from instructions you have executed may mean you now need different instructions, negating the gain by fetching and decoding others before.

Small memory cells that operate at a higj speed. They store data and operations are carried out on data in them

An electronic device which generates signals, switching between 0 and 1. The clock speed is measured in Hz

An independent processor able to carry out its own F/D/E cycle