CLASSIFICATION OF DIGITAL COMPUTERS:

Computers are classified according to size speed and memory capacity. Computers are of different types:

• Super Computers


• Main frame Computers


• Mini frame Computers


• Micro/PC/Desktop


• Laptop

Super Computers:
Super Computers are the largest, faster, and the most expensive computer system in the world. They are used to process complex scientific jobs. They are considered to be the resources (assets) of any nation. Super Computer are used to performed million of instructions at the same time. Very few companies in the world produce super computers. Cray research and ETA systems are two primary manufacturers of super computers in the United States. Fujitsu, Hitachi and NEC are the companies in japan, which produce super computers.
Use of the Super Computers:
Super computers are widely used in meteorological where weather patterns are predicted by manipulating vast amount of data.
Mainframe Computers:
The Mainframe Computers are the large computers available in different models, capacities and prices etc.
Examples: IBM 370, DEC 1090 and NEC etc.
Characteristics of Mainframe Computer
The main characteristics are:

• They are based on the principle of strong physical computing power. Many people can make use of the same machine at the same time.
• They are sensitive to variations in temperature, humidity, dust etc., and are hence in a controlled environment, i.e., air conditioned rooms.
• Qualified operators and programmers are required for their operations. They support
• Wide range of peripherals.
• They have a large storage capacity.
• They can make a use of wide range of software
• These systems generally support 500 to 2000 local and remote users

Mini Computers:
Mini Computers were introduced in the 1960s. They have less capacity to manipulate and store data, compared to mainframe computers. Examples: Digital Equipment Company (DEC) introduces first Mini frame computer called VAX.
Characteristics of Mini Computers
Some of the characteristic of minicomputers are:

• They offer limited range of peripherals.
• Limited software can be used.
• There is facility for direct operation of the machine by the end user
• Air conditioning is not necessary for minicomputers.
• Computers are widely used for data processing and in industry.
• These system generally support 10 to 200 users.

The Micro / Personal / Desktop Computers:
These computers are used now days commonly and these computers revolutionized the Computer industry because of their size and cost.
Some of the features are:

• They are cheap and easy to use
  
• They have limited input and output capacity
• They have low storage capacity
• The range of the software that can be used by one person at a time
  
• A visual display screen or a printer is used to get the output

Uses of the Microcomputers:
Most of the companies produced microcomputers. They are used for various applications. They are also used by million of a persons for entertainment and personal applications.
Laptop Computers:
There are light and compact and are called portable because they work on batteries and can operate without external power source. Laptop, which weigh from four to eight pound, are often called notebook PCs because they are about the size of a one-inch think notebook. These computers are fits in briefcase and they do not have to plug in. Most laptops accept diskettes, so it is easy to move data form one computer to another. Normally these computers are expensive.

HYBRID COMPUTERS:

A computer that combines the characteristics of both analog and digital computer is known as hybrid Computer. Example of a hybrid computer system a cement plant where all calculations are made by digital computers and action such as increase in material, or decrease of fuel for temperature is performed by the help of analog computers.
Example 2:
In ICU ( Intensive Care Unit ) of hospital Hybrid Computers are used. Analog quality of these Computer controls the temperature of the room and Digital quality of these Computers informs to doctor about the blood pressure, temperature and physicalstatus of the patient.
Characteristics of Hybrid Computers:

1. These Computers are reliable and provide accurate result.
2. These Computers work fast and speedy.
3. Both analog and digital qualities are present in these Computers.
4. These Computers are helpful in Hospitals.

DIGITAL COMPUTERS:

Digital means discrete (single). With digital signals, every thing is described in two states either on or off. Computer is based on principles of counting. Infact, digital computers use digital signals, which can distinguish between just two values 0 and 1.
Characteristics of Didital Computers:

1. Digital Computers have two staes on (1) and off (0).
2. These Computers are very easy to use and operate.
3. Human being likes to use Digital Computers.
4. These Computers are reliable in result.
5. These Computers have big memory.

These Conputers are further divided into different categories such as

Personal Computers, Mainframe Computers, Mini frame Computers, Laptop Computers, Super Computers etc.

ANALOG COMPUTER:

The computer that consist of mechanical parts, having needle-dial meters speedometers, quartz clocks or watches are called ANALOG COMPUTERS. Analog computers operate by measuring rather than counting. The output of those computers is normally in continuesform. Normally, these are used at weight machines, petrol pumps and in Industrial or plant accessories like boilers and oil filling sections.
Characteristics of Analog Computers:

1. The speed of Analog Computer is fast.
2. The result of these Computer is not reliable.
3. These Computers became the bases for Digital Computers.
4. These Computers are difficult to use and operate.
5. THese Computers are asy-.tu..deelop.
6. These Computers have small memory

Different Types of Programming Language

Programming languages are divided into following three distinct categories.

1. Low Level Language
2. High Level Language
3. IDE ( Integrated Development Environment)

Low Level Language:
Programming language that normally translates from one source instruction to onne-object instructions.
These languages are machine dependent, The program or instructions written in these languages are in binary from and are very close to the machine language.
The main Low Level Language are:
Machine Language:
machine language is a language that a computer can understand.
OR
A low-level language that is directly understandable by the computer system. Each model of a computer has a unique machine language. It is the fundamental language of computer and is written in the form of binary strings 1's and 0's. The programs written to machine language are very fast in execution. there are no limitations of Machine language. All types of high level programming language are also developed of Machine language. It is difficult to learn programming language because to learn this language, detailed knowledge of Hardware is required. It is also a time consuming method of programming. If there is any error in a program written in this language, it is difficult to find out the error. This language is machine dependent. To write an application program in this language, a programmer has to write a program according to internal structure of computer.
Assembly Language:
A low level programming language in which mnemonics are used to code operations and alphanumeric symbols are used for addresses. This language lies between high level language and machine language. Assembly language is very close to the machine language and was developed in 1950. In this language symbols are used instead of binary numbers. This language is, therefor, also called the symbolic language.In this language mnemonic codes are used in place of 1s and 0s to written a program 9or instructions). A mnemonic code is an alphabetical abbreviation used to represent the machine code instructions. For example, to represent an addition operation, a programmer might use the mnemonic AD. Assembly is used to convert the program written in assembly language into machine code.
High Level Language:
A programming language whose structure is application oriented and is independent of the structure of the computer is called High Level Language.
OR
The programming language that is easy to understand for human being but difficult for machine due to frequent use of commonly used English Words is called High Level Language. Each statement of such a language is translated into many machine language statement. Sets of instructions are written in English words that are quite easy to understand which are then translated into machine language. The ease of high-level language provides many programmers a in past few years. A program written in High-Level Language an be executed on any computer, which has compiler is system software, which is used to translate program written in high level language into the machine executable form.
Integrated Development Environment (IDE) (Language);
IDE is the latest kind of programming that has become most popular over the last few years. These language provides a visual environment of working in which user feels more pleasant to work and develop programs. The most significant aspect of these modern development facilities is that they provide a very large number of preprogrammed facilities to their programmers, which can simply be chosen by pointing and dragging certain pictures and icons on the screen that reduces the programming time. The IDEs infect provides a hybrid environment of the procedural and object oriented languages. Many user friendly and visual working facilities are grouped together in IDE.

What is Programming Language

PROGRAMMING LANGUAGE:
A language used to express algorithms in computer understandable form. Programming language is the process of giving instructions to the computer so that the machine can execute the given task. It's the way of communicating with computers. Programming languages are used to prepare customize application / software for the people. Although a large variety of application software have, spread out rapidly which meet certain problems of the computer users. Quite often, a special program has to be developed that meets the specific needs of a company for which any other application software is not available.
Programming language are used to develop such specific application that meets the requirements of the company precisely. The procedure of developing a computer program by using a programming language is known as" Programmer". A programmer must follow the predefined rules and regulations of a particular language, which is called "Syntax" of the language.

Different kinds of Operating System

The most commonly used operating systems are:
MS-DOS ( Microsoft Operating System )
MS-WINDOWS Microsoft Windows ) (95, 98,2000, xp etc.)
UNIX and LINUX
WINDOWS NT ( New Technology ).
NOS ( Network Operating System ).
SUN SOLARIES
ZINIX / MINIX
OS/2
NET WARE
Mac. OS ( Macintosh Operating System ).
CLASSIFICATION OF OPERATING SYSTEM:
The operating system can be classified as:

1. Single-user operating system,
2. Multi-user operating system,
3. Single-tasking operating system,
4. Multi-tasking operating system,

Single-user Operating System:
Single-user operating system means only one user may log into the system at a time. These operating systems are used on individual computers. this kind of computer system is used only on personal computers. Some of the most widely used single-user operating system.

• MS-DOS
• OS/2
• Macintosh system etc.
• Windows 95 & 98

Multi-user Operating System:
Multi-user operating system means more than one can log into the computer at a time. These operating system are usually used on computers, which are lying over LAN in an office or company. Multi-user Operating System are used on large computers systems for commercial scientific and engineering data processing purposes.
Some of the multi-user operating systems are:

• UNIX / XENIX
• Novell
• Windows NT

Single-tasking Operating System:
The opertaing system on which just a single task can be performed at a time is called single tasking operating system. These operating system are no longer popular now, For example,

• MS-DOS

Multi-tasking Operating System:
The operating system which multi tasks (operation) can be performed at a time is called multi tasking operating system. These operating system have become extremely popular
due to high accessibility options. For example

• UNIX
• WINDOWS
  OS / 2 etc

GUI Operating System:
GUI stands for Graphical User Interface. Windows is a GUI operating system because it provides a visual environment with Command Buttons, Icons, Menus and different color combination. Windows is easy to learn because its graphical interface is consistent from one application to another. People previous using DOS they now prefer to use latest version of UNIX and Windows, Which are GUI operating systems. However Gui systems usually have the disadvantage of requiring more hardware such as CPU, more memory ( RAM ), higher quality monitors etc.