CPU

CPU

1. The purpose and function of a CPU (Processor) is to fetch, decode and execute instructions (process data) in a computer system

2. Components of the CPU

   • Cache
     • Stores frequently/commonly used data
     • Acts as a intermediary between the processor and RAM
     • Larger Cache = Faster Processing; Saves fetching the instructions and data repeatedly from RAM – a relatively slow process which keeps the CPU waiting otherwise
   • ALU
     • Arithmetic Logic Unit performs arithmetic calculations (e.g. Numbers) and logic functions (>,<,=,!=).
   • Control Unit
     • Controls the flow of data transfers between CPU and the timing of operations in the computer.
     • Checks that information have been delivered successfully between hardware/CPU

3. The “brains” of the computer; Computer cannot run without it

4. Stores Data into Main Memory once instructions are executed

5. Factors which affect the CPU's Performance

   • Cache Size
     • Larger Cache = Faster Processing
     • Has 3 levels
       • L1 - Usually part of the CPU already and is the smallest and the fastest cache to be accessed
         • L2 & L3 - Extra Caches that can be built between the CPU and the RAM. The more L2 and L3 memory available, the faster a computer can run. However, L2 and L3 cache takes slightly longer to access than L1 because it's further away from the CPU than L1
   • Clock Speed
     • How fast the computer is at executing instructions per second
     • Measured in Hertz
       • 1GHz Processor executes 1 Billion Instructions per second
         • 2GHz = 2 Billion 4GHz = 4 Billion etc.
       • Number of Cycles per second
   • Cores
     • The purpose of Cores is to allow more instructions to be done simultaneously
     • Processors can have multi-cores
       • Dual Core Quad Core 8 Core
       • The amount of cores multiplies the number of instructions which can be executed
         • e.g. 2GHz Single Core Processor executes 2 Billion Instructions 2GHz Quad Core Processor executes 8 Billion Instructions 2x4 = 8

6. Central Processing Unit

7. POST (Power-On-Self-Test)

   • A program used In the BIOS chip (Basic Input/Output System) which checks that all hardware and software is running properly
   • A message is sent to the monitor if the hardware/software isn't working properly
   • Happens when the computer system is 'booted up' (turned on)