Central Processing Unit (CPU)

Architecture and components of computer systems

 

The internal architectural design of computers differs from one system model to another. However, the basic organization remains the same for all computer systems. The following five units (also called "The functional units") correspond to the five basic operations performed by all computer systems.

Input Unit

Data and instructions must enter the computer system before any computation can be performed on the supplied data. The input unit that links the external environment with the computer system performs this task. Data and instructions enter input units in forms that depend upon the particular device used. For example, data is entered from a keyboard in a manner similar to typing, and this differs from the way in which data is entered through a mouse, which is another type of input device. However, regardless of the form in which they receive their inputs, all input devices must provide a computer with data that are transformed into the binary codes that the primary memory of the computer is designed to accept. This transformation is accomplished by units that called input interfaces. Input interfaces are designed to match the unique physical or electrical characteristics of input devices to the requirements of the computer system.

See Also: Types of Computers by purpose

In short, an input unit performs the following functions.

1. It accepts (or reads) the list of instructions and data from the outside world.

2. It converts these instructions and data in computer acceptable format.

3. It supplies the converted instructions and data to the computer system for further processing.

Output Unit

The job of an output unit is just the reverse of that of an input unit. It supplied information and results of computation to the outside world. Thus it links the computer with the external environment. As computers work with binary code, the results produced are also in the binary form. Hence, before supplying the results to the outside world, it must be converted to human acceptable (readable) form. This task is accomplished by units called output interfaces.

In short, the following functions are performed by an output unit.

1. It accepts the results produced by the computer which are in coded form and hence cannot be easily understood by us.

2. It converts these coded results to human acceptable (readable) form.

3. It supplied the converted results to the outside world.

Storage Unit

The data and instructions that are entered into the computer system through input units have to be stored inside the computer before the actual processing starts. Similarly, the results produced by the computer after processing must also be kept somewhere inside the computer system before being passed on to the output units. Moreover, the intermediate results produced by the computer must also be preserved for ongoing processing. The Storage Unit or the primary / main storage of a computer system is designed to do all these things. It provides space for storing data and instructions, space for intermediate results and also space for the final results.

In short, the specific functions of the storage unit are to store:

1. All the data to be processed and the instruction required for processing (received from input devices).

2. Intermediate results of processing.

3. Final results of processing before these results are released to an output device.

See Also: Characteristics of a Computer

Central Processing Unit (CPU)

The main unit inside the computer is the CPU. This unit is responsible for all events inside the computer. It controls all internal and external devices, performs " Arithmetic and Logical operations". The operations a Microprocessor performs are called "instruction set" of this processor. The instruction set is “hard wired” in the CPU and determines the machine language for the CPU. The more complicated the instruction set is, the slower the CPU works. Processors differed from one another by the instruction set. If the same program can run on two different computer brands they are said to be compatible. Programs written for IBM compatible computers will not run on Apple computers because these two architectures are not compatible.

The control Unit and the Arithmetic and Logic unit of a computer system are jointly known as the Central Processing Unit (CPU). The CPU is the brain of any computer system. In a human body, all major decisions are taken by the brain and the other parts of the body function as directed by the brain. Similarly, in a computer system, all major calculations and comparisons are made inside the CPU and the CPU is also responsible for activating and controlling the operations of other units of a computer system.