Cpu

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CPU- brain of the computer
Purpose- process data
Searching, sorting, calculating, decision making
Every task dealt with by CPU

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3 components:
Control Unit
Arithmetic and Logic Unit
Immediate Access Store

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Programs like word processor, even games, made up of machine code; must be followed for the program to work
Humans only can write simple instructions as they're stored as a series of numbers.

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Programmers write the source code in languages- C++
Translated into machine code so the CPU can understand; .exe files

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FETCH-DECODE-EXECUTE CYCLE
1. Fetch:
First step CPU carries out; fetch some data and instructions from main memory then store in their own internal temporary memory areas- registers.
CPU makes use of a vital hardware path- the address bus

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CPU places address of the next item onto the address bus
Data from this address moves from main memory to the CPU by travelling along another hardware bus- data bus

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2. Decode:
Next step is for the CPU to make sense of the newly fetched information- Decode
The CPU is designed to understand a specific set of commands- instruction set of the CPU. Each make of CPU has a different instruction set
The CPU decodes the instructions, prepares various areas within the chip to get ready for the next step.

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3. Execute:
Processing actually takes place. The instruction is carried out upon the data. The result is processing and is stored in yet another register.
Once this stage is complete, the CPU sets itself up to begin another cycle

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THE CONTROL UNIT
1- it controls and monitors the hardware attached to the system to make sure the commands given to it by the application software are used.
2. Controls the input and output of data so the signals go to the right place at the right time.
3. Controls the flow of data within the CPU which is essentially the fetch-executive.

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THE IMMEDIATE ACCESS STORE:
Often referred to as RAM as it is the technology chiefly associated with it.
The name reflects the fact the data can be read from anywhere in the IAS without going through all the memory addresses.
This holds the data and instructions needed that instant by thhe CU
The CPU reads the data and programs held on backing storage and stores them in temporary memory
The CPU needs to do this as the backing storage is too slow to run applications directly.

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ARITHMETIC AND LOGIC UNIT:
Computer exchanges data by manipulating it or acting upon it
1. Arithmetic part- does exactly what you think it should do- performs sums on the data
2. Logic comparisons- deals with logic and comparisons. Compares data items such as numbers, letters or special characters to see if they meet a particular condition
3. Logic Function- based on boolean algebra. Used to compare numbers which can only be a 1 or a 0, which are normally used to present true or false
3 Basic Types:
-OR
-AND
-NOT

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CLOCK SPEED:
Computers can only do one thing at a time although it may appear many things are happening simultaneously.
The computer only processes one instruction at a time- its so fast you think it's happening at once
A CPU processes digital data by taking each piece of data one-at-a-time and doing something with it. The amount of time it has to process each piece of data is controlled by a quartz inside the CPU

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With every tick, the computer can process one piece of data or execute one instruction.
The CPU clock speed is measured in cycles- 1 cycle per second=1 Hertz.
A computer running at 1Ghz can carry out 1 thousand million instructions per second
The clock on a modern desktop computer runs extremely quickly, typically 3Ghz

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It's hard to imagine how fast this is, but it means the CPU running at this clock speed can handle a huge amount of data in a very short time
Clock speed higher- faster performance, but runs hotter and consumes more power
Clock speed lower- lower performance, but less costly and less power used- good for battery life in laptops.
Over-clocking- some people try to get the most extreme performance out of their CPU by adjusting the clock to run faster than the CPU was designed for, making the CPU hotter and extra cooling fans need to be bought.

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THE CACHE:
Most data's stored on the hard disk. When we use that data it is loaded into RAM as it is much faster to access the data from RAM than from the hard disk.
RAM is faster than the hard dick, but still cannot cope with the speed the CPU needs to deal with
To avoid this you store as much data as possible as close to the CPU to avoid delays. This nearby storage is called cache
Can be accessed faster than RAM. The CPU looks in the cache for the data it needs.

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It will retrieve and process the data if it is there, but if not the CPU accesses the system memory and puts a copy of the new data in the cache before processing it.
Cache memory is volatile
To improve the computers performance, the cache should always be full so the CPU doesn't have to wait around with nothing to do.
The larger the cache size, the better the performance

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RAM- temporary memory. Works fairly safe here while the computer is working but when it is shut down everything disappears- volatile.
As well as storing the data tou're working on, RAM stores the modules needed to make your apps work.

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It is also needed so you can have multiple windows open and switch between them.
If you have a lot running at once, you might find your system starts to slow down as your RAM is full and is having to decide what it needs to keep stored in memory at any given time and what it can release. If this happens often, you can improve the performance by installing extra RAM.

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ROM:
Special type of memory which stores the instructions the computer uses when it 'boots up' the BIOS.
It allows to check the type of hard disk installed, the type of CPU being used etc.
As the data is 'read only' it cannot be written to.

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The ROM chip (there may be more than one) is attached to the motherboard.
The key thing to remember is the data is not erased when the computer is switched off- the data is stored permanently- non-volatile.