1.2 Computer systems

A computer is an electronic device that performs calculations on data, presenting the results to humans or other computers in a variety of (hopefully useful) ways. The computer system includes not only the hardware, but also software that are necessary to make the computer function.

Computer hardware is the physical part of a computer, including the digital circuitry, as distinguished from the computer software that executes within the hardware.

Computer software is a general term used to describe a collection of computer programs, procedures and documentation that perform some task on a computer system

Computer organization

General model of a computer

A computer performs basically five major operations or functions irrespective of their size and make.

1. Input: This is the process of entering data and programs in to the computer system. You should know that computer is an electronic machine like any other machine which takes as inputs raw data and performs some processing giving out processed data. Therefore, the input unit takes data from us to the computer in an organized manner for processing.

2. Storage : The process of saving data and instructions permanently is known as storage. Data has to be fed into the system before the actual processing starts. It is because the processing speed of Central Processing Unit (CPU) is so fast that the data has to be provided to CPU with the same speed. Therefore the data is first stored in the storage unit for faster access and processing. This storage unit or the primary storage of the computer system is designed to do the above functionality. It provides space for storing data and instructions.

The storage unit performs the following major functions:

- All data and instructions are stored here before and after processing.

- Intermediate results of processing are also stored here.

3. Processing : The task of performing operations like arithmetic and logical operations is called processing. The Central Processing Unit (CPU) takes data and instructions from the storage unit and makes all sorts of calculations based on the instructions given and the type of data provided. It is then sent back to the storage unit.

4. Output : This is the process of producing results from the data for getting useful information. Similarly the output produced by the computer after processing must also be kept somewhere inside the computer before being given to you in human readable form. Again the output is also stored inside the computer for further processing.

5. Control : The manner how instructions are executed and the above operations are performed. Controlling of all operations like input, processing and output are performed by control unit. It takes care of step by step processing of all operations in side the computer.

In order to carry out the operations mentioned above, the computer allocates the task between its various functional units. The computer system is divided into several units for its operation.

• CPU (central processing unit) : The place where decisions are made, computations are performed, and input/output requests are delegated
• Memory: stores information being processed by the CPU
• Input devices : allows people to supply information to computers
• Output devices : allows people to receive information from computers
• Buses : a bus is a subsystem that transfers data or power between computer components inside a computer.