Computer Processor. How Stuff Works


When you think of purchasing a Computer, the first choice you have to make is, the best processor type because the Processing unit is the most important part of the Computer. The speed of computer, performance, multitasking ability, all depends on the processor. The CPU or the Processor is the Brain of computer allowing to process numeric data and executing the instructions stored in the memory. The Processor operates at the speed of an internal clock that sends pulses called Peaks. The clock speed called cycle is the number of pulses per second which  is represented in Hertz. With each peak of pulse, the processor performs a function based on the instruction. The term Cycles Per Instruction or CPI represents the average number of clock cycles required for the processor to execute an instruction. The latest version of processor is the family of Duo Core in which two processing units are present. Core duo was the first series by the Intel and Core 2 Duo is the next version. The Core 2 brand was introduced on July 27 ,2006 comprising Solo, Duo, Quad and Extreme sub brands.

The Processor requires four steps to complete the process of an action. These are Fetch, Decode, Execute and Write back.

1. Fetch is the process by which an instruction from the memory is retrieved. The location in programme memory is determined by the Programme counter that stores a number that identifies the current position in the memory. Once the instruction is fetched, the programme counter is incremented by the length of the instruction word in terms of memory units. This instruction fetched from the memory is used to determine the action of CPU.

The instruction has two fields like Operation code that represents the action that the processor must execute and the Operand code that represents the parameters of action. The instructions may be Memory access ( to access a memory), Arithmetic operation( addition, multiplication, deletion, subtraction etc), Logic operation( AND,OR,NOT etc) and Control ( sequence of controls) etc. After executing the instruction, the processor will store the instruction in 8, 16, 32 or 64 bits as memory. These are called Registers. Cache memory or Buffer memory denotes the local memory that reduces the waiting time for the information from the RAM.

2. The Decoding step involves the breaking of the instruction into parts that have significance to other parts of the CPU. The Microprogramme is used to assist to translate the instruction into various configuration signals for the CPU.

3. After the fetching and Decoding, the execution takes place in which various portions of CPU are connected to perform the desired operation. The Execution unit completes the tasks assigned by the instruction unit. It has elements like Arithmetical and Logic Unit or ALU, Floating Point Unit or FPU, Status register and Accumulator register.

4. Finally during the Write back step, the result of the execution is converted into some form of memory. After completing all the steps, the processor goes into the next cycle.