What is CPU

 What is CPU?

Central Processing Unit – CPU

The CPU is the centrepiece of any modern day computer.  They are the small piece of silicon that everything revolves around. Located on your motherboard usually with a heat-sink-fan over it, the CPU does all the calculating and a lot of the data transfer in your computer. Most processors nowadays would be considered microprocessors, and if they run a computer they are CPU’s.  They can be networked, distributed systems, multiprocessors, or multicomputers.  Which all involves parallel programming.  The framework of a computer consists of the processor, memory, input and output units. The processor has the following components.

Arithmetic-Logic-Unit

The arithmetic - logic unit (ALU)  performs  all arithmetic    operations    (addition,  subtraction, multiplication,   and   division)   and   logic   operations. Logic operations test various conditions encountered during processing and allow for different actions to be taken based on the results. The data required to perform the arithmetic and logical functions are inputs from the designated CPU registers and operands. The ALU relies on basic items to perform its operations.  These include number systems, data routing circuits (adders/subtracters), timing, instructions, operands, and registers.

Program Counter

Contains the memory address of the next instruction to be executed.

Control Unit

Coordinates all the activities taking place in the CPU, the memory and added peripherals.  It does this by sending control signals to the devices.

Current Instruction Register

Contains the current instruction to be run.

Status Register

Contains information about interrupts but also contains the output of the previous instruction, a different bit would be set for a different results. From this the CPU would decide if to branch out of a given sequence.

Memory Address Register

Holds the address of the memory location from which data will be read or to which data will be written. The MAR may sometimes hold the address of the instruction to be read.

General Purpose Registers

Used for performing arithmetic functions, CPUs can contain only one or a number of general purpose registers.  A set of instructions could be the following where the numbers are memory locations.

1. Load contents of 1000 into the accumulator.
2. Add the contents of 1001 to the accumulator.
3. Store contents of accumulator in 1002.

Memory data register or Memory buffer register

Used to temporarily store information read from or written to the memory. All transfers from memory to the CPU go via the memory data register. Serving as a buffer region to compensate for the difference in speed between the CPU and memory.

The frequency at which a processor (CPU) operates is determined by applying a clock multiplier to the front side bus (FSB) speed.  For example, a processor running at 550 MHz might be using a 100 MHz FSB.  This means there is an internal clock multiplier setting of 5.5; the CPU is to run at 5.5 times frequency of the front side bus: 100 MHz x 5.5 = 550 MHz.  By varying either the FSB or the multiplier, different CPU speeds can be achieved.