COMPUTERS

1. INTRODUCTION TO COMPUTERS Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

2. Study Note developed by S. Agarwal, Lecturer & Systems Incharge, St. Xavier’s Computer Centre St. Xavier’s College Kolkata July-2002 Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

3. What is a computer ? A computer is an electronic device capable of performing arithmetic and logical operations. It can also store a large volume of information. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

4. Arithmetic operations involve the general mathematical calculations like addition, subtraction, multiplication and division. Logical operations involve comparisions like > < = etc. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

5. How does a computer work? INPUT  PROCESS  OUTPUT INPUT consists of DATA & INSTRUCTION. PROCESS is a set of instructions stored in the computer to carry out the instructions given by the user. The process is also called a PROGRAM. OUTPUT is the set of results generated after processing the Input. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

6. DATA & INFORMATION DATA is described as some FACTS, FIGURES and STATISTICS about a particular instance. For example : MARKS in individual subjects. INFORMATION is some FACTS, FIGURES and STATISTICS which help us in decision making. Generally information is the result of data processing. For example : PERCENTAGE & GRADE. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

7. HARDWARE Hardware are the PHYSICAL COMPONENTS of the Computer System. Examples : All the electronic parts. All cables. All accessories. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

8. SOFTWARE SOFTWARE are the logical components of the computer system. These are basically the programs and information stored in the computer. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

9. The hardware and software can be better explained with the help of a music system. Hardware : The device, cassette, tape, wires etc. Software : The music stored in the tapes. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

10. Characteristics of Computer SPEED STORAGE ACCURACY VERSATILITY AUTOMATION DILIGENCE Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

11. SPEED The speed with which the computer works can be understood by the units of measurement of time within a computer. They are : MILLI SECOND – 1/1000THOF A SECOND MICRO SECOND – 1/1000THOF A MILLI SECOND NANO SECOND – 1/1000THOF A MICRO SECOND PICO SECOND – 1/1000THOF A NANO SECOND Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

12. STORAGE As already discussed a computer can store a large volume of information. The factors to be considered for storage are : • RETREIVAL – IMMEDIATE • SPACE – VERY LITTLE • MEDIA – MAGNETIC MEDIA • LONGIVITY – FOR EVER Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

13. ACCURACY The accuracy of the computers is consistently high. Errors in the machinery may occur, but due to efficient error-detecting techniques, these very seldom lead to wrong results. Errors in computing are due to human rather than technological weaknesses. So, we can say that A COMPUTER NEVER MAKES ANY MISTAKE Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

14. VERSATILITY • Computers seem capable of performing any task, provided the task can be broken to a series of logical steps. • The computer actually performs only four basic operations : • Exchanges information with the outside world via INPUT / OUTPUT devices • Transfers data within the computer to the different units • Performs basic arithmetical operations • Performs operations of comparison • We can reduce the daily activities into steps of the above operations with the help of Programming. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

15. AUTOMATION Once a program to perform a particular task is stored in the computer, the individual instructions in the program are carried out one after the other automatically to complete the task. Hence the user requires to just press certain keys and give the data input. The data is automatically processed to produce the output. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

16. DILIGENCE Being a machine, a computer does not suffer from the human traits of tiredness and lack of concentration. If 5 million calculations are to be performed, it will perform all of them, even the last one with exactly the same accuracy and speed. In fact, there are some computers which are constantly on for hours, days, months and years are never switched off. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

17. ANATOMY OF THE COMPUTER BASIC STRUCTURE The computer receives input, processes it and delivers output. To perform these tasks it has different units and each unit is responsible for a specific task. The units are INPUT, MEMORY, CONTROL UNIT (CU), ARITHMETIC & LOGIC UNIT (ALU) AND OUTPUT. The CU and ALU together are called CENTRAL PROCESSING UNIT (CPU). Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

18. INPUT DEVICE It is used for transferring data from the users’ end to the computer. OUTPUT DEVICE It is used to transfer processed information from the computer to the user in a way required by the user. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

19. MEMORY UNIT It stores instruction and data and provides them to the various other units as and when required. It is basically the working memory of the computer system. This memory unit is volatile, i.e. it is temporary memory and nothing can be stored here permanently. The information is stored in the main memory as long the computer is switched on or as long as it is required by the computer. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

20. CONTROL UNIT Controls the various operations within a computer. It basically manages all the other units and devices of the computer system. It does so by transmitting timing and control signals to the various devices and units. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

21. ARITHMETIC & LOGIC UNIT It performs the various arithmetic and logical operations on the data stored in memory, as dictated by the instruction. There are various basic circuits to perform these operations. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

22. SECONDARY STORAGE It stores the various data, information and programs permanently for future retrieval. The information is organised in such a way to retrieve it in minimum time whenever required. The stored information remains as long the user wants it. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

23. BUS These are a set of connecting wires used for setting interconnection between the various devices in the system. Each set of bus has a specific function to perform like carrying data, carrying control signals and addresses. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

24. BLOCK DIAGRAM DATA FLOW CONTROL FLOW SECONDARY STORAGE OUTPUT DEVICE INPUT DEVICE MEMORY UNIT CONTROL UNIT ARITHMETIC & LOGIC UNIT CPU Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

25. A character is the smallest amount of information that can be communicated to the computer. All data, information and instruction are represented by a combination of these characters. DATA REPRESENTATION WITHIN A COMPUTER CHARACTER : All alphabets, digits and symbols are characters. Even a blank space is a character. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

26. How does the computer understand a character? Computer being an electronic device, can represent only two states – VOLTAGE and NO VOLTAGE. Voltage is represented as 1 No voltage is represented as 0 Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

27. 1 0 1 1 1 0 0 1 A series of such 0s and 1s form a pattern. Such a pattern represents a CHARACTER. For each character a separate pattern is there within the computer. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

28. 1 0 1 1 1 0 0 1 There are eight such positions to represent 0 or 1 and each such position is called a BIT. Hence the pattern generated to represent a character is a BIT PATTERN. BIT Two digits, 0 and 1 can generate 256 unique combinations if represented in eight places. Hence we can represent 256 different characters in any computer. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

29. ASCII American Standard Code for Information Interchange. It is difficult for us to remember all the 256 bit patterns and their corresponding characters. Hence we can convert the bit pattern to a decimal number. This way each bit pattern will have a different number and this number, fixed for a character is called the ASCII code of the character. All computers follow the same ASCII code and bit pattern to represent characters. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

30. BINARY The number system involving two digits, 0 & 1 is called BINARY. By using this system a bit pattern (treated as a binary number) can be converted to the decimal number system. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

31. 0 27 26 25 32 16 24 23 8 22 21 20 1 = 57 0 0 1 1 1 0 1 • Starting from right to left, raise 2 to the power of 0 to 7. • Add the values corresponding to the BIT positions having the value 1. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

32. 0 0 27 27 27 128 27 26 26 26 26 25 25 32 25 25 32 24 24 24 16 24 8 23 23 23 23 8 22 22 22 22 21 21 21 21 1 20 20 20 20 1 = 185 = 41 1 0 0 1 0 0 0 1 1 1 1 0 1 1 0 0 0 1 1 1 0 0 1 0 0 1 1 1 0 128 64 32 16 8 4 2 1 = 255 = 0 1 Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

33. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

34. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

35. UNIT FOR MEASUREMENT OF INFORMATION 8 BIT = 1 CHARACTER = 1 BYTE 1024 BYTES = 1 KILO BYTE (KB) 1024 KB = 1 MEGA BYTE (MB) 1024 MB = 1 GIGA BYTE (GB) 1024 GB = 1 TERA BYTE (TB) Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

36. HARDWARE Input devices : KEYBOARD : It is an input device to give character based inputs to the computer. All types of data, instruction and information can be given through the keyboard. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

37. Although the typing portion of the computer keyboard is identical to a standard typewriter, computers have several additional keys that perform different functions. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

38. MOUSE : It is used for graphics based inputs. It can mainly select some graphical icons and select some options from a menu. It can not be used for giving data to the computer. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

39. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

40. SCANNER : It is used for graphical inputs. Pictures, images, drawings etc. can be scanned and stored in the computer. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

41. Operation of the SCANNER : On the simplest level, a scanner is a device which converts light (which we see when we look at something) into 0s and 1s (a computer-readable format). In other word, scanners convert analogue data into digital data. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

42. DIFFERENT INPUT TYPES MICR : Magnetic Ink Character Recognition. This system uses highly stylized character shapes printed in an ink containing magnetic particles. These characters pre-printed in magnetic ink are recognised by a device called MICR reader. Mainly used in Bank Cheques. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

43. MICR CHEQUE NUMBER Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

44. OMR : Optical Mark Reading Forms and cards are pre-printed for special purposes so that a mark can be made in a specified position. Each mark at a position has a specific meaning and after scanning, the data gets transferred to computer. Mainly used in correcting answers to Multiple Choice Question Papers. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

45. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

46. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

47. BAR-CODE RECOGNITION : Lines or bars can be arranged in a code and are used particularly for labelling goods etc. Bar-code reading is performed by a scanner. A sequence of bits is generated and the information is recorded. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

48. BAR CODE FOR PRODUCT CODE Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

49. VOICE INPUT : This system accepts spoken input. The waveform created by the input is analysed, patterns are extracted and matched against pre-stored patterns to identify the input. The words and phrases the system is to recognise, are spoken with the system and the patterns are created for future matching. For the voice of more than one person, training with the system must be done separately. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.

50. OUTPUT DEVICES VDU : Visual Display Unit. Also called a monitor or a screen. It a device similar to a TV screen. The output on a VDU is temporary. Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's College, Kolkata.