Definition of Computer, it's Type and Basic Structure of Digital Computer, System Software, Programming Languages

What is a Computer? 

Basically, it is a fast calculating machine which is nowadays used for the variety of uses ranging from household works to space technology. The credit of the invention of this machine goes to the English Mathematician Charles Babbage.

Types of Computer:
A. Based on nature, computers are classified into:

  1. Analog computers:
    Analog computers deal with measuring physical quantities (concerned with continuous variables). Analog computers are nowadays rarely used.
  2.  Digital computers:
    The digital computer operates by counting and it deals with the discrete variables. There is a combined form called Hybrid computer, which has both features.
Continuous and Discrete Variables:
Continuous variables are those which don't have fix value or vary continuously. For example: if you say you are 20 years old, but actually you may be 20 years, 15 days old, or you are 20 years, 15 days, 10 hours years old, or it can be even countable in additional minutes, seconds or milliseconds.  

While Discrete variables are those which have fix value. For example: If I gave you 1000 rupees, then you will have exactly 1000 rupees but not 1000.20 or 1000.222220. 

Analog and digital clocks are also of similar meaning. Your clock hung on a wall of the room or in your wrist watch with Hour hand, Minute hand, and Second hand fall in continuous variables and are the analog clocks. While the time in your mobile phone generally used or some blink watches which gives time in the form of 12:00:00 fall under digital type.

Basic Structure of a Digital Computer
The von Neumann architecture, which is also known as the von Neumann model and Princeton architecture, is a computer architecture based on that described in 1945 by the mathematician and physicist John von Neumann. This describes a design architecture for an electronic digital computer with parts consisting of a processing unit containing an arithmetic logic unit and processor registers; a control unit containing an instruction register and program counter; a memory to store both data and instructions; external mass storage; and input and output mechanisms. The key idea of the Von Neumann architecture is the stored program concept. A stored-program digital computer is one that keeps its program instructions, as well as its data, in read-write, random-access memory (RAM). Stored-program computers were an advancement over the program-controlled computers of the 1940s.

Figure: Block Diagram of Computer

The main components of a computer are Input unit (IU), Central Processing unit (CPU) and Output unit (OU). The information like data, programs etc. are passed to the computer through input devices. The keyboard, mouse, floppy disk, CD, DVD, joystick etc. are certain input devices. The output device is to get information from a computer after processing. VDU (Visual Display Unit), Printer, Floppy disk, CD etc are output devices. The brain of a computer is the CPU. It has three components- Memory unit, Control unit and Arithmetic and Logical unit (ALU).

The memory unit also called as the storage device is to store information. Two types of memory are there on a computer. They are RAM (random access memory) and ROM (read-only memory). When a program is called, it is loaded and processed in RAM. When the computer is switched off, whatever stored in RAM will be deleted. So it is a temporary memory. Whereas ROM is a permanent memory, where data, program etc are stored for future use. Inside a computer, there is a storage device called Hard disk, where data are stored and can be accessed at any time. 

The control unit is for controlling the execution and interpreting of instructions stored in the memory. ALU is the unit where the arithmetic and logical operations are performed. The information to a computer is transformed into groups of binary digits, called bit. The length of bit varies from computer to computer, from 8 to 64. A group of 8 bits is called a Byte and a byte generally represents one alphanumeric ( Alphabets and Numerals) character. The physical components of a computer are called hardware. But for the machine to work it requires certain programs ( A set of instructions is called a program ). They are called software. There are two types of software, System software, and Application software. System software includes Operating systems, Utility programs, and Language processors. 

Operating System:

The set of instructions which resides in the computer and governs the system are called operating systems, without which the machine will never function. They are the medium of communication between a computer and the user. DOS, Windows, Linux, Unix, android system etc are Operating Systems. 

Utility Programs:
These programs are developed by the manufacturer for the users to do various tasks. Word, Excel, Photoshop, Paint etc are some of them.

Programming Language: 
1. Low-level Language:

Low-level languages are machine level and assembly level language. In machine level language computer only understand digital numbers i.e. in the form of 0 and 1. So, the instruction given to the computer is in the form binary digit, which is difficult to implement instruction in binary code. This type of program is not portable, difficult to maintain and also error-prone.

The assembly language is, on the other hand, a modified version of machine level language. Where instructions are given in English like the word as ADD, SUM, MOV etc. It is easy to write and understand but it is hard for the computer to understand. So the translator used here is assembler to translate into machine level. Although language is bit easier, the programmer has to know low-level details related to low-level language. In the assembly level language, the data are stored in the computer register, which varies for a different computer. Hence it is not portable.

2. High-level Language

These languages are machine independent, means it is portable. The language in this category is Pascal, Cobol, Fortran etc. High-level languages are not understood by the machine. So it needs to translate by the translator into machine level. A translator is a software which is used to translate high-level language as well as low-level language into machine level language.

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