What is CPU?

In order to work, a computer needs some sort of "brain" or "calculator". At the core of every computer is a device roughly the size of a large postage stamp. This device is known as the central processing unit (CPU). This is the "brain" of the computer. It is the part of a computer that interprets and carries out the instructions contained in the software. In most CPUs, this task is divided between a control unit that directs program flow and one or more execution units that perform operations on data. Almost always, a collection of registers is included to hold operands and intermediate results.

When every part of a CPU is on a single physical integrated circuit, it is called a microprocessor. Practically all CPUs manufacturered today are microprocessors.

The term CPU is often used vaguely to include other centrally important parts of a computer such as caches and input/output controllers, especially when those functions are on the same microprocessor chip as the CPU.


What does the CPU do?

CPU carries out instructions and tells the rest of the computer system what to do. This is done by the Control Unit of the CPU, which sends command signals to the other components of the system.

Performs arithmetic calculations and data manipulation, e.g. sorting, combining, etc. The part of calculation of CPU is call Arithmetic Logic Unit (ALU)


Arithmetic Logic Unit (ALU)

l The arithmetic logic unit executes arithmetic and logical operations. The arithmetic operations include addition, subtraction, multiplication and division. The logical operations compare numbers, letters and special characters. The comparison operations test for three conditions are equal-to condition in which two values are the same, less-than condition in which one value is smaller than the other, greater-than condition in which one value is larger than the other.

l Relational operations are used to describe the comparison operations used by the arithmetic logic unit. The arithmetic logic unit performs logic functions such as AND, OR and NOT.


Control Unit

The control unit directs the entire computer system to carry out stored program instructions. It must communicate with both the arithmetic logic unit and main memory. It use the instruction contained in the instruction Register to decide which circuits need to be activated. Control unit co-ordinates the activities of the other two units and all peripheral and auxiliary storage devices linked to the computer. control unit instructs the ALU which arithmetic operations or logical operation is to be performed.



Cache is random access memory ( RAM) that a computer microprocessor can access more quickly than it can access regular RAM. As the microprocessor processes data, it looks first in the cache memory and if it finds the data there, it does not have to do the more time-consuming reading of data from larger memory.

Cache memory is sometimes described in levels of closeness and accessibility to the microprocessor. An L1 cache is on the same chip as the microprocessor. L2 is usually a separate static RAM (SRAM) chip. The main RAM is usually a dynamic RAM (RAM) chip.


How does the CPU work?

The CPU is centrally located on the motherboard. Since the CPU carries out a large share of the work in the computer, data pass continually through it. The data come from the RAM and the units . After processing, the data is sent back to the RAM and the units.

The CPU continually receives instructions to be executed. Each instruction is a data processing order. The work itself consists mostly of calculations and data transport.