What Is a Computer?

1. A computer is a machine having an intricate network of electronic circuits.

2. We can make computer do what we want by inputting signals.

3. Computers accept information in the form of instructions called a program and characters called data.

4. Computers have three basic capabilities.

5. First, computers have circuits for performing arithmetic operations.

6. Second, computers are used for controlling directly things such as robots.

7. Third, computers have circuits that can make decisions.

8. A computer can solve a series of problems and make hundreds, even thousands of logical decisions without becoming tired or bored.

9. That is why a computer can replace people in dull, routine tasks.

10. But it works according to the instructions given to it.

Basic Functional Units of Computers

1. The basic concepts are essentially the same for all classes of computers.

2. A computer consists of five functionally independent main parts, namely, input, memory, arithmetic and logic, output, and control units.

3. The input unit accepts coded information from humans, from electromagnetic devices, or from other computers.

4. The information can be stored in the memory for later reference.

5. Or it can be handled by the arithmetic and logic circuitry.

6. The results are sent back through the output unit.

7. These actions are coordinated by the control unit.

8. The arithmetic and logic circuits in conjunction with the main control circuit are referred to as a central processing unit.

9. Input and output equipment is usually combined under the term input / output unit.

10. The simplest example is the terminal consisting of a keyboard for input and a display for output.

Input and Output Devices

1. Input and output devices attached to a computer are referred to as peripheral devices.

2. The simplest of input devices is the keyboard.

3. Whenever a key is depressed the corresponding letter or digit is automatically translated into its corresponding code.

4. The mouse facilitates work with your PC.

5. Its primary functions are to help user to draw, point, and select images on the computer display.

6. A very fast way of inputting information is its scanning using optical character recognition.

7. Voice recognition is a technology which is limited in its present form, but it shows great promise for the future.

8. The most common output device is the VDU (Visual Display Unit).

9. Printer is an output device which changes output data into printed form.

10. Printers are still very slow compared to the electronic speeds of a processor unit.

General Features of Operating Systems

1. An Operating System (OS) is a master control program which controls the functions of the computer system as a whole and the running of application programs.

2. Computers usually process several programs concurrently.

3. This is said to be multiprogramming.

4. In multi-user environment an OS controls terminal operations on a shared access basis.

5. The OS allocates control to each terminal in turn.

6. Some environments operate in concurrent batch and real-time mode.

7. This means that a background job deals with routine batch processing while the foreground job deals with real-time operations.

8. The OS interrupts batch processing operations to deal with real-time enquires or file updates.

9. The stage of batch processing attained at the time of the interrupt is temporarily transferred to backing storage.

10. After the real-time operation has been dealt with, processing recommences from a “restart” point.

11. The OS also copies to disk backing storage the state of the real-time system every few minutes (periodic check points).

12. It provides a means of recovering the system in the event of a malfunction.