Computer needs to receive data and instruction in order to solve problems therefore we need to input data and instruction into computer. The input unit consists of one or more input devices. All the input devices perform the following functions. (1) Accept data and instruction from outside world (2) convert it to a form that the computer can understand. Supply the converted data to the computer system for further processing.
The storage unit of computer holds data and instruction that are entered through the input unit before they are processed. It preserves the intermediate and final results before these are sent to the output devices. Storage devices of computer system are categorized as:
- Primary storage – Stores plus provides data very fast. This memory is generally used to hold the program being currently executed in the computer. The data being received from the input unit, the intermediate and final programme. The primary memory is temporary in nature. The cost of primary storage is more than secondary storage
- Secondary storage – Secondary storage is like an archive. It stores several programme, documents, data, etc. The programmes that you run on computer are first transferred to the primary memory before it is actually run.
- Arithmetic Logic Unit – All calculations are performed in ALU of computer. It also does comparison and takes decision. The ALU can perform basic operations such as addition, subtraction, multiplications, etc. and does logic operations. Logic operates on whenever calculations are required. The control unit transfers the data from storage unit to ALU once the computations are done. The results are then transferred to the storage unit and then it is sent to the output unit for displaying result.
- Control unit – It controls all the other units in computer. The control unit instructs the input unit where to store the data after receiving it from user. It controls flow of data and instruction from the storage unit to ALU.
- CPU – The control unit and ALU are together known as CPU. It performs calculations and takes decisions and controls all the unit of a computer.
The output unit is the unit where the result of instructions given and processed is seen. The monitor screen is the output unit of the computer.