Ict Cpu

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CPU - Central Processing Unit
CPU is:
the brain of the computer
Purpose - processing data
where all:
SEARCHING, SORTING, CALCULATING and DECISION MAKING is done.

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Components of the CPU:
1.Control Unit (CU) - controls hardware and software, preforms fetch-decode-execute cycle.

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2. Arithmetic and Logic unit (ALU) - preforms calculations, comparisons of values and Boolean operations.
3.Immediate Access Store (IAS) - holds data and programs currently in use.

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GENERAL PURPOSE COMPUTER:
RAM - Random Access Memory

Control Unit - controls the sequence of events that needs to happen.

ALU - Arithmetic Logic Unit

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Fetch-Decode-Excecute Cycle:
all programs are made up of simple instructions called the 'Machine Code' these must be followed in order for the programe to work.
humans are only able to write simple instructions in this form.

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programmers then write the source codeine languages such as C++, Java or Dephi.
this is then translated into machine code, the format that the CPU can understand, often referred to as .exe files.
the Fetch-Decode-Execute Cycle standard process describes the steps needed for processing to take place.

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1. Fetch
CPU fetches some data and instructions from main memory then stores it in it's own internal temporary memory, these areas are called 'Registers'.
For this to happen, CPU makes use of a vital hardware path called the 'Address Bus'.

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CPU places address of the next item on the address bus.
data from this address moves from main memory to CPU by traveling along the 'Data bus'

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2. Decode
next step is the CPU has to make sense of instructions it has just fetched.
process is called DECODE.
CPU designed to understand a specific set of commands, called the 'instruction set' of the CPU.
each CPU has a different instruction set.
CPU decodes the instructions and prepares various areas within the chip in readiness of the next step.

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3. Execute
part of the cycle when data processing takes place. the instruction is carried out on the data.
the result of this is stored in another register.
once the execute stage is complete the CPU sets itself up again for another cycle.

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The Control Unit:
3 main jobs:
1. controls and monitors hardware attached to the system to make sure the commands given to it by the application software are used.

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2. control the input and output of data, so that signals go to the right place at the right time.
3. controls the flow of data within the CPU which is the fetch-decode-execute cycle.

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The IAS - Immediate Access Store:
often referred to as the RAM as it is the technology chiefly associated with it.
data can be read form anywhere in the IAS without going through all the memory addresses.
holds the data and instructions needed that instant by the CPU.

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CPU reads data and programs held on backing storage and stores them.
CPU needs to do this because backing storage is much to slow to be able to run the applications directly.
data and programs are first of all loaded into the main memory, then the CPU fetches just the part it immediately needs and loads it into it's own internal registers

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The Arithmetic and Logic Unit (ALU):
this is where the computer processes data either by manipulating it or acting upon, it consists of 3 parts:
1. Arithmetic part - it preforms calculations on the data.
2. Logic comparisons - deals with logic and comparisons, it compares data items such as numbers, letters or special characters to see if they meet a particular condition.

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3. Logical functions - based on Boolean algebra, used to compare numbers which can only be 1 or 0, which are usually used to mean 'true' or 'false.
there are 3 basic types:
1. the OR functions
2. the AND functions
3. the NOT functions

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Clock Speed:
computers can only do one thing at a time, it may appear the many things are yapping simultaneously, but in reality a computer can only process on instruction at a time, just because the computer is so fast, everything seems to be happening at once.

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CPU processes digital data by taking each piece of data one-at-a-time and doing something with it. a quartz clock controls the time the CPU has to process each piece.
with every tick of the clock, CPU is able to process one piece of data or execute one instruction.

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CPU clock speed is measured in cycles per second, 1 cycle per second is known as 1 hertz.
a computer running at 1GHz can carry out 1 thousand million instructions per second.

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the clock on a modern desktop computer runs extremely quickly, typically 3 thousand millions times a second.
the faster the CPU, the more powerful the computer.

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CPU clock speed is measured in cycles per second, 1 cycle per second is known as 1 hertz.
a computer running at 1GHz can carry out 1 thousand million instructions per second.

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the clock on a modern desktop computer runs extremely quickly, typically 3 thousand millions times a second.
the faster the CPU, the more powerful the computer.

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Clock speed higher - faster performance but runs hotter and consumes more power.
Clock speed lower - lower performance, less costly, needs less power - so good for battery life.

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Over Clocking - some people try to get the most extreme performance out of their CPU. they do this by over clocking, this means that they adjust the clock to run faster than the CPU was designed for, this makes the CPU hotter and so extra cooling are needed.

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The cache:
data is stored on the hard disk.
when we use data it is loaded in to the RAM, faster to access data in RAM than Hard Disk.
RAM is faster that the hard disk, but RAM is not fast enough to cope with the speed that the CPU has to deal with.

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the way around this is to store as much data as possible as close to the CPU to avoid delays, this is called 'cache'
cache can be accessed faster than RAM.

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CPU looks first in the cache for the data it needs. if the data is there it will retrive it and process it.
if the data isnt there, CPU access the system memory and puts a copy in the cache before processing it.

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Cache memory is Volatile.
to improve the computers preformance its important to keep the local cache full.
Larger cache size = Better preformance, because data can be stored locally.

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RAM:
Volatile.
RAM stores data that you are working on, it stores the modules needed to make the application work.
RAM is needed to have multiple windows open so you can switch between them.
if alot of windows are open, your computer may slow down, this is becasue RAM is full, you can improve the preformance by installing new RAM.

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ROM:
stores instructions which the computer uses when it boots up -The BIOS.
ROM allows to chech the type of hard disk and CPU used.
READ ONLY, it is non-volatile.
ROM chip it attached to the motherboard.