Digital Computer ? Advantages-Disadvantages Diagram

A digital computer is an electronics device that read the data from the environment through the input device,

General Block Diagram of a Digital Computer
General Block Diagram of a Digital Computer

Digital Computer

We are familiar with a word, ‘Compute’ which means to calculate. The term computer is derived from the word ‘Compute’. The computer is a device or machine that performs pre-defined or programmed computations or controls operations that are expressible in numerical or logical terms at a high speed with great accuracy. It is used to store, transfer and transform information.

A digital computer is an electronics device that read the data from the environment through the input device, store them in a memory, process them according to the command given by the user (programmer) and display the result or output to the environment through the output unit. A computer can process data, pictures, sound and graphics etc. they can solve highly complicated problems quickly and accurately. A computer mainly performs five major computer operations or functions irrespective of their size and make. The figure 1.3 shows the general block diagram of digital computer. It consist of Arithmetic and Logic Unit (ALU), control unit, input unit, output unit and memory (Storage) unit.

  1. It accepts data or instruction by way of input
  2. It stores data
  3. It can process data as required by the user
  4. It gives result in the form of output
  5. It controls all operations inside a computer

Block diagram of digital computer

 General Block Diagram of a Digital Computer
General Block Diagram of a Digital Computer

The solid line arrow indicates the flow of data and instruction (—-)

The dashed line indicates the flow of control from control unit ( ——- )

Input Unit

  • Input unit read the instructions and the data from the user with the help of input devices such as keyboard, mouse, microphone etc.
  • It converts these instruction and data in computer acceptable form
  • It supplies the converted instruction and data to the computer system for further processing

Output Unit

  • Output unit accepts the result produced by the computer, which is in the coded form and cannot be accepted by user
  • It converts these coded result into the human readable form
  • It supplies the converted result to the user with the help of output devices such as VDU, speaker, printer, plotter etc.

Storage Unit

  • The storage unit stores the instruction and the data
  • All data and instructions are stored in storage unit before and after processing
  •  It is also used to store the intermediate result (which are generate after a computation)
  •  There are two types of storage unit used in a computer. They are primary and secondary memory. Primary memory is also known as internal memory, main memory, semiconductor memory, combination of RAM and ROM. Similarly, Secondary memory is also known as external memory, auxiliary memory, backup memory etc.

1. Primary Memory

Primary memory is a main memory of a computer and it is volatile in nature. If the power of a computer is switched off the unsaved data from the primary memory is lost. RAM is an example of main memory. Primary memories are faster in nature and it is expensive compared to secondary memory.It is directly connect to the processor. Example of primary memory are register memory and cache memory. The following figure 1.4 shows example of memory Hierarchy. As we go down in the memory hierarchy the following thing will occur:

– Decreasing cost per bit.
– Decreasing the storage speed or performance.
– Decreasing the frequency of access of the memory by the processor.

Memory Hierarchy
Memory Hierarchy


2. Secondary Memory

Secondary memory is an auxiliary memory of a computer and it is non-volatile in nature. Even though if the power of a computer is off the data stored in auxiliary memory will not be lost (i.e. permanent in nature). ROM (Read Only Memory), Flash drive, Hard disk, Magnetic tape, optical disk etc are auxiliary memory. Secondary memory is not directly connected to the processor. Secondary memories are slower in nature and it is cheap as compared to primary memory. The example of secondary memory are magnetic disk, hard disk, pen drive, optical disk, CD ROM, DVD, Blu-ray disk etc.

     Central Processing Unit

The central processing unit (CPU) is the brain of a computer system. All the major calculations And comparisons are made inside the CPU. The CPU is also responsible tbr actirating and controlling the operations of other units of the computer system.

1. ALU (Arithmetic Logic Unit)

The actual processing of the data and insffuction are performed by Arithmetic Logic Unit. The major operations performed by the ALU are addition, Subtrrctior, multiplication, division, logic and comparisons. Data is transferred to ALU from storage unit when  required. After processing the output is return back to storage unit for fuither processing.

2. CU (Control Unit)

CU controls all the operations performed in a computer. The operations like input, processing and output are controlled by control unit. It takes care of step by step processing of all operations inside the computer. The control unit determines the sequence in which computer programs and instructions are executed. Things like processing of programs stored in the main memory, interpretation of the instructions and issuing of signals for other units of the computer to execute them. Control Unit acts like the supervisor seeing that things are done in proper fashion.

1.2.1. Advantages and Disadvantages of Digital System

    Advantages of digital system 

  • Have made possible many scientific, industrial, and commercial advances that would have been unattainable otherwise.
  •  Less expensive .
  • More reliable .
  • Easy to manipulate .
  • Flexibility and Compatibility
  •  Information storage can be easier in digital computer systems than in analog ones. New features can often be added to a digital system more easily too.

   Disadvantages of digital system

  • Use more energy than analog circuits to accomplish the same tasks, thus producing more heat as well.
  •  Digital circuits are often fragile, in that if a single piece of digital data is lost or misinterpreted, the meaning of large blocks of related data can completely change.
  •  Digital computer manipulates discrete elements of information by means of a binary code.
  •  Quantization error during analog signal sampling.


Types of computers





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