Central Processing Unit (CPU)

Central Processing Unit (CPU)

1. What is it?

   • Often referred to as the brain of the computer. It is a microprocessor thats main role is to process programs and data. it does this by using Fetch- Excetute cycle.

2. The main components

   • Conrol Unit.
     • This component manages the excecution of instructions using the Fetch- execute cycle. It does this by sending control signals to other parts of the cpu. Its main jobs are: - Fetching and deciding what instructions to carry out, Decode the instructions and then follow or execute the instructions
   • Arithmetic and logic unit (ALU)
     • Processes data that requires arthimetic calculations. This includes addition, subtraction, division and multipication. It also perfroms logical comparisons to assist with decision making.
   • Immediate Access store (IAS)
     • Also referred to as main memory, this component stores all data and programs temporarily when in use or on External storage devices permanently. During Fetch-Execute cycles, Instructions are fetched from the IAS using a unique address each memeory location has.

3. Fetch - Execute Cycle

   • The Cpu has a a number of registers which are high speed memory locatations.
     • Program Counter (PC)
       • This CPU register stores the address of the next instruction to be fetched as many programs are ordered in sequence. For this to work the program counter is automatically incremated by 1 everytime an intruction is fetched.
     • Memory Address Register. (MAR)
       • The address of any instruction or data being used are stored in here.
     • Memory Data Register(MDR)
       • Temporaily stores data ebing fetched from the IAS. All data transferred from IAS to the Cpu goes via the MDR.
     • Instruction Register (IR)
       • Temporarily stores the current instructions being decoded.
     • Accumaltor
       • Part of the ALU. When calculations take place on data, the results are stored here before being transferred to the IAS. It is the default location of calculation performed by the ALU.

4. Factors that influence processing speed

   • Clock Speed
     • An indicator of the speed which a CPU can operate and is measured in GHz (Gigahertz). It represents how many instrcution cycles a CPU can handle. The default setting is often maximum clock speed but increasing or decreasing the clock speed will not change the processor.
   • Cache
     • Is used to temporarily store frequently used instructions. It has a small capacity memory and is between the Processor and the RAM. The CPU will automatcally check CACHE first when fetching a instruction as it has a lower storage unit. This increases the processing speed.
   • Processor Core
     • A core is a a single processorwith its own CPU, ALU and registers. A dual core CPU will have two processors. This increases there ability to run more programs at the same time.

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