Cpu Notes

Front 1

The CPU is the brain of the computer, Its purpose is to process the data.
This is where all the searching, sorting, calculating and decision making happens.

Back 1

The CPU has 3 main components
- CU (Control unit) performs the fetch-Decode-Execute Cycle.

- IAS (immediate access store) holds data and progams in use for quick access

-ALU (Arithmetic and logic Unit) performs all the computers' calculations

Front 2

Fetch-Decode-Execute-Cycle

Although most users are unaware of it, all programs from word processors to games, are made up of a series of simple instructions called MACHINE CODE that must be followed in order for the program to work

Back 2

1. Fetch

The cpu fetches some data and instructions from main memory to store tem in their own internal temporary memore areas called registers.
For this to happen the CPU makes use of a hardware path called the address bus.
The CPU places the address of next item on the 'ADDRESS BUS'
Data from this address then moves from main memory to the CPU through the DATA BUS

Front 3

2. Decode

This step is for the CPU to make sense of the imformation.
The CPU is designed to understand a specifc set of commands. These are called 'instructions set' of the CPU.
The CPU then decodes them and prepares various areas within the chips.

Back 3

3. Execute

Data processing takes place here. The instructions are then executed on the data. The result of this is tored in another register
Once this is complete the CPU begins another cycle.

Front 4

IAS(Immediate Access Store)
Holds data and instructions needed that instant by the CU.The CPU reads data and programs and saves them temporarily to the IAS. Often referred to as RAM.
Cpu reads the data and programs held on backing storage and stores them temporarily in the IAS memory.
The CPU needs to do this because backing storage is to slow to run applications directly.
Data and programs loaded into main memory, CPU fetches just the part it immediatley needs and loads it into its own internal registers.

Back 4

The ALU (Aritmetic Logic Unit)
Where the computer manipulates the data
This consists of 3 parts:

1. Aritmetic part - e.g 3+2=5

2. Logic comparisons - this deals with logic and comparisons and compares data items to see if they meet a certain condition.

3. Logical Functions - These are based on Boolean Algerbra. Compares numbers which can only be 1 or 0 which usually mean TRUE or False
3 basic types:
-OR
-AND
-NOT

Front 5

Clock Speed

Computers can only do one thing at a time. It may appareas that many things are happening simultaneously.

The computer can only process one instruction at a time.

Back 5

The CPU proccess each pice of data one at a tme. This is controlled by a quartz clock inside the CPU
With each tick the CPU is able to process one pice of data.
1 cycle per second is known as 1 Hertz
It runs 3,000,000 times a second (3GHz)
The speed of the clock intially determines the performance of the CPU

Front 6

Higher - Higher Clock speed, faster performance but runs hotter and consumes less power
Lower - Less costly, needs less power

Over Clocking - adjusting the clock to run faster than the CPU was designed for makes it hotter so extra cooling fans are needed

Back 6

The Cache

Although RAM is faster than the hard disk, it is not fast enough to cope with the speed the CPU needs to deal with
This is overcome by the closely placed are called "Cache"
Much faster than RAM
Volatile
Important to keep cache full to improve the computer's performance.
Larger Cache = Better performance

Front 7

RAM
Temporary Memory, when switched off it all dissappears.
Needed so you can have multiple windows open
The more windows open, the slower the computer as the RAM is full up.
Can be improved by adding extra RAM

Back 7

ROM
Special type of memory
Basic Input Output System (BIOS) used for boot-up
Allows it to check the type of hard disk, CPU etc.
Non-editable
ROM Chip attatched to Motherboard
Non-volatile memory (permanent)