History of Computers

History of Computers

1.Abacus: the Chinese invented this in 600 B.C. This is also called soroban. The beads on the racks represent the numbers. This calculating device is mainly for addition and subtraction.

2. John Napier's Bone: john Napier invented this in 17 the century. This was also called "cardboard multiplication".

3. Punched Cards: This calculating device is used to store the data in the form of punches on the cards. This was used as input device.

4. Analytical Engine: This device does all the operation that the modern computers do. This was invented by Charles Babbage in 1822. This device doesn't meet the necessity requirement and he came up with the new idea called "Difference Engine" 1842. So, he is called the "Father of Modern Digital Computers"

5. MARK1: This device was invented in 1937, this was used for all calculation. This was also called Automatic Sequence Controlled Calculator.

6.ENIAC : Electronic Numerical Integrator And Calculator. This was invented in 1943. This was the first Electronic device in its time.

7. EDVAC : Electronic Discrete Variable Automatic Computer : This was invented in 1946. The basic idea was to storage of data that directs the flow of controls.

8. EDSAC : Electronic Delay Storage Automatic Computer. This was in 1947. This device simultaneously invented by the British.

9. UNIAC : Universal Advanced Computer.


GENERATION OF COMPUTERS.
Generation represents the "development in the Technology". There is mainly four generation and it is divided in the development in the technology.

First Generation:
In this generation Vacuum tubes were used to develop any computer.
1. The size of the computer was large.
2. Vacuum tubes were used.
3. Produces large amount of heat because of many vacuum tubes.
4. Difficult to repair because of frequent hardware failure.
5. Cost was high.
6. Large rooms with A/C were required.



Second Generation:
In this generation Vacuum tubes were replaced with transistors.

1. Size of the computer decreased compared with the first generation.
2. Transistors were used.
3. More reliable.
4. Less hardware failure.
5. Cost decreased compared to first generation
6. Produces less heat.

THIRD GENERATION
Some groups of transistors were placed in a silicon chip called IC's (Integrated Circuits).
1. More reliable than first and second generation of computers
2. IC's called Integrated Circuits were used.
3. Less hard ware failure compared to both generation
4. Cost decreases
5. Mainly used for commercial purpose.
6. A/C not required due to less heat.

FOURTH GENERATION
In this generation IC's also called Small Scale Integrated Circuits were removed and Medium scale Integrated Circuits and Large Scale Integrated Circuits were used.

1. Less cost
2. The size decreased.
3. No hardware failure.

TYPES OF COMPUTERS:
Computers are divided in to three types.

1. Analog computers: This type of computers process the data in variable quanties. For example in the petrol pumps, analog processors are used, the flow of fuel is converted into quantites and price values. This analog computers are cheap and easy to program. They are not accurate.

2. Digital Computer: Computers of this type process the data in numerals. They accept numbers, letters, symbols,etc. The values are accurate. They are used in banks.

3. Hybrid computers: This type of computers is the combination of analog and digital computers. It got the best features of both the type.

Computers are characterized in functions.
1. Special purpose computers: These computers are also called dedicated computers. Some sets of instruction were feeded to do a specific job according to that instructions. So, they can do only
a particular job.

2. General Purpose Computers: This type of computers can do any application. It is not restricted to a particular task.

Computers can be categorized to physical sizes. In first generation of computers a huge computer was used to do a simple operation and now it became a desktop size and works faster than the previous generations.

There are some computers, which differ in their sizes.
1. Super computer: Super computers are fastest and largest computers. They accept many processors and no. of jobs can be done at a time. It accepts no. of users do to different tasks. It uses many secondary storage devices like magnetic tapes, cd's, etc,
It has a huge capacity to store the processed data. It is mainly used in defense and weather research, etc. ILLIAC IV was the first super computer. Some other examples are CRAY, PARAM, fujitsu,etc,

2. Mainframe Computers: These computers accept multiple processors, and it accepts or many terminals can connected to it. It must have a high speed printers, many input / output devices.
It processes the complex type of data and also has the capacity to hold huge database. It is used in large banks, airlines for the storage of the database.

3. Mini Computers: Mini computers are smaller in size. It can accept many terminals. It has the capacity to store the processed data. It is a commercial purpose computer.

4. Micro Computers: It is also called Personal computers. The size of this computer is smaller than mini and mainframe computers. Its main input device is keyboard. Mouse used as pointing device. It has less storage capacity compared to super and mainframe computers.

Basic Computer Organization:
There are five basic operations. They are
1. Inputting
2. Outputting
3. Control unit
4. Storage unit
5. Processing

1. input: This operation is used to feed the information in the computer. The standard devices are keyboard, Mouse-a pointing device, and card redirect. The input devices must accept the data from the outside world and the computer to process it must accept the same data. The data or information feuded through the keyboard are stored in the storage device.

2. OUTPUT: This operation is used to display the feeded data or the processed data. Some standard output devices are monitor or screen, printer, etc. These output devices must accept the data, which was processed by the processor. The processing is done binary format and it must be converted to understandable form.

3. Control Unit: This unit is used to control all the devices, which is helpful for processing. It controls the inflow and outflow of data. It works like a traffic cop, which controls the movement of data from memory to processing unit. We can also say it as central nervous system of the computer. Because it controls and co-ordinates all the devices. It must accept the value returned by the ALU and also by the memory.

4. Storage Unit: Storage unit is to store any kind of information. Whatever the data inserted or feeded through keyboard is first stored in the memory for further processing. It must store the intermediate results and also final result. The memory in the storage unit is divided in the form of cells. Each and every cell has its address.
Memory is divided in two types.

RAM: Random Access Memory. It is a type of memory, which access randomly. All the values are not stored sequentially. This type of memory is also called Read/Write memory. That means the values are stored as well as it can be retrieved from the memory. There are two types of RAM.

(I) Static RAM
(ii) Dynamic RAM

(i) Static RAM: Values are stored throughout the process. It consumes more power.
(ii) Dynamic RAM : Data stored in this memory must be refreshed in every milliseconds. Otherwise the values are erased off. It consumes less power and it is it's advantage.

b. ROM: Read Only Memory. The content in this memory is mainly used for reading purpose. The program cannot be altered, added, or modified by the user.
PROM : Programmable Read Only Memory. This is similar to ROM.
EPROM: Erasable Programmable Read Only Memory. This type of ROM is used to make changes in the ROM contents. The programs must be deleted everything and new program must be added. Some portion of the program cannot be altered. Whole program must be deleted and fresh or new Program must be loaded in the ROM chip.

EEPROM : Electrically Erasable Programmable Read Only Memory: ROM chip of this type used to erased a small portion of the program with the help of high voltage.

Processing: Processing is done in Arithmetic Logical Unit (ALU). Any kind of data stored in the memory flow through control unit to ALU for processing are again stores the result in the memory, which flows to control Unit. The combination of control unit and the ALU is called Processor.


SECONDARY STORAGE DEVICES:
The values, programs or the contents in file are basically stored in primary devices called hard disk or local disk. Some other storage devices called secondary storage devices used to store the values. They are also used for transportation of data.

1. Punched Paper cards: This type of storaging data is used in the form of punched holes. The paper card is in the form of rolls and it width is of one inch. The values are stored in row wise. The punched holes in the form of rows are called channels. So, each row in the card represents a character.

2. Floppy Disks: This type of storage devices are commonly used now a days. The disk is made of plastic cover coated with magnetic oxide, and it is covered with hard plastic cover. Disk is divided in the form of tracks and in sector wise. The data is stored in the tracks in sector wise.

3. Winchester Disk: Winchester disk is closed in a hard cover and it is not recommended to open. A special type of lubricant is used to reduce the friction when the head pointer moves to read the data.

4. Optical Readers: This type of input devices is used to read the special characters, marks, printed characters, etc. This is a special device which the marks with the reflection of light.

a) OMR : Optical Mark Reader. This device is used to read the marks, bars, or any other special character or symbols.
For example, to read the rate of the products, a bar code reader is used to read the bars available on the product's cover.
OMR sheets are used to dark the marks wherever necessary so that the mark reader reads the dark objects as it's input.

b) OCR : Optical character Reader. This is used to read only hand written characters, printed characters. The hand written character must be in standard width, height,etc. There shouldn't be any loops as we write in running letters. The printed characters must be in standard font and size.

Output devices:

1. Visual Display Unit (VDU): This is the most common device used with microcomputers. It is having the technology of CRT, which is also used in television. CRT - Cathode Ray Tube. It displays the character on the screen instead of on papers. The printed text is also called softcopy. The screen varies in different sizes. Normally the screen has 24 lines and 80 characters.

2. Plotters:
Plotters are used to produce designs and graphs. There are basically two types : a) Drum plotter b) Flatbed plotters.
a) Drum Plotters: It is having a drum in which the paper is fixed and it is moved to and fro which makes it in vertical motions.
The pens are clamped in the holder with different set of colors and they are moved in horizontal directions. When the both move simultaneously the graphs or design are produced on the paper.

b) Flatbed Plotters: In this type of plotters the paper is not fixed and set of colored pens are in motion. These are controlled by the computer.
Plotters are normally slow because it is marked up lots of mechanism as compared to the speed of computers.

3) Printers: Printers are of two types. They are impact and non-impact printers.
a) Impact Printers: This type of printers normally leaves the impression of the characters on the paper.
b) Non-Impact Printers: Printers of this type are quiet and fast and they don't leave any impression.

a) Impact printers: These are of two types, character printers and line printers.
Character printers: In this type of printers one character is printed at a time. For example, a typewriter, which prints one character at a time.
Some examples of character printers are:
1) Letter-Quality printer: This is of impact printers having a set of font wheels also known as daisy wheel. This wheel is set to rotate at a high speed. And whenever the desired character is required, a hammer which is behind the paper strikes the paper. 10-50 characters are printed in a second.

2)Dot-Matrix Printers: These printers print each character as a pattern of dots. The print head had matrix of tiny needles. The print quality is inferior to letter-quality printers but faster than it. These printers are less expensive as compared to daisy wheel. These printers can print any shape characters as described by the printer.

3)Ink-Jet Printers: These are non-impact printers which prints the characters by spraying small drops of ink onto paper. It produces high quality output because the characters are formed by dozens of tiny ink dots. They are quiet and form any shape of characters.

Line Printers: Line printers are impact printers used with large computer system to produce huge output. They are fast printers.
Drum Printers and Chain Printers are commonly used.

1) Drum Printer: Drum printers are consists of a solid, cylindrical drum that has raised characters in bands of its surface. There are many bands and it rotates at high speed. When the desired character appears, the hammer strikes the paper along with the ribbon which is behind it. One revolution is required to print one line.

2) Chain Printers: They use rapidly moving chains called print chain. As the print chain rotates, there is a print hammer located behind the paper and when it founds the desired character it strikes on the paper along with the inked ribbon.

Page Printers: Page printers are non-impact printers, which can produce documents with a high speed. For example, xerography, lasers and other technologies. These techniques called electro photographic techniques. Printers of this type are extremely fast and cost effective.

Computer Software:
It is a set of programs written in a language in order to control the applications.

Basically three types of software’s:
1. System software
2. Application software
3. General-Purpose software.

1. System Software:
This type of software is related to system, for example to control the process of printers, floppy, media devices, etc.
System software include the following options:
a) Programming Language
b) Translators
c) Modules
d) Operating system

a) Programming Language: These are some set of instructions given to system in a systematic manner in order to get the desired output.
Machine level or Low level Language: This language is related to machine understandable code. i.e., only machines can understand easily but not the user. It does all the manipulation in BITS (Binary Digits). 0's and 1’s, so combination of bits represents a number or character.

Assembly Level Programming Language: In this type of languages the code are written in mnumonic which are the combination of letters-symbols. It is also a machine dependent.

High-level language: This user-friendly language, i.e. the user can understand the language easily but the system fails to understand it. So, we use translators to translate high level language to machine level.

b) Translators: Translators are used to convert the source code written in high level to low level. Assembler translates the source code written in assembly level to machine level. Compilers and Interpreters convert the source code in High level to low level. Compilers compile the source code all at once. Where’s the interpreters interprets one statement at a time.

c) Modules: Modules are set of instructions to do a specific task. So, group of modules constitute a program. A separate module does a specific task.

d) Operating System: Operating system acts as an interface between the user and the hardware. It manages the users request and also the hardware components. It acts like a manager.

2) Application Software:
It is special software used to do some specific job. Like the employee payroll, so the software deals with only the payroll application, railway reservation is also one of the examples, which uses the details about the train and about the reservation details, and it is also used for scientific calculations used by the researchers.

3. General Purpose Software:
This type of software executes only one function, which is mostly used in the offices. Like word processing, spreadsheets, database management, graphics, etc.

Number System:
Number system is used to convert the numbers in the form of bits. Here 0's and 1's are called bits or binary digits. Zero indicate "false" or "Off" and One indicates "True" or "ON"
Types of Number Systems:
1. Binary Digits - base 2
2. Decimal - base 100
3. Octal - base 8
4. Hexa Decimal - base 16

Disk Operating System (DOS):
Dos is a layer of programs which controls the system components and the files. It acts like an interface between user and the hardware. It is like a manager, which manages the system resources as well as the user's request.

[draw the diagram ]

In the diagram the Operating system acts like a mediator to the user and the hardware. If the user wants a file, he will request the o/s and the O/S accepts the request and searches the file in the hardware and again responds to the user. Here the O/s does interact directly with the hardware.

Features:
1. Multitasking: Task is any kind of job. Multitasking represents to no. of jobs which the o/s can handle at time. Some o/s can handle many tasks to do. For example Unix, Linux, windows NT, 2000 Server, etc.,
Ms-Dos is a single tasking o/s, which can do only one job at a time. After the completion of a task it moves to another job to do.

2. Multi-User: Multi-user operating system supports many users at a time. It can accepts many user's job at a time and can process it. For example, Linux, Unix, etc, and Ms-dos supports only single user. It can accept one user's request and after completion of the job it moves to another user.

3. Multi-Threading: Thread represents functions or a self-contained block of statements that has a specific task to do. Some operating system supports multi-threading that can do all the functions simultaneously.

4. Time Sharing: This is the method where all the multi-tasking operating system works to do a sequence of jobs given at a time. If some group of jobs is given by number of users, the operating system sets a priority of the jobs, and allocates time for each job.