Classification Of Computers

 

In the 1970s computers were classified into three categories, namely, super-computers, large computers and mini computers. But the invention of the micro-processor which gave birth to micro-computers in the late 70s has drastically changed the computing scene. A wide range of computers are available today in the market ranging from a personal computer to a super computer.

 

A personal computer (PC) is a micro-computer which has its entire central processing unit on a single micro-processor chip. A PC provides a main memory capacity upto 640 kilo bytes and a processing power of 0.5 MIPS. It supports one or 2 diskette drives of 360 KB each for random access secondary memory. A PC usually comes with a standard key board, a visual display unit and a dot matrix printer. A PC is usually operated by a single user.

 

A super mico-computer has its entire central processing unit on a very powerful micro-processor, provides a main memory capacity of upto 16 mega bytes, has a processing power of 2 to 3 MIPS, supports Winchester disks of capacity 20 to 80 mega bytes and allows simultaneously access to multiple users. Today’s super micro is actually replacing yesterday’s mini computers which provide almost the same computing power it nit less, but based on a different technology.

COMPUTER SOFTWARE

Today we are going to discuss on Computer Software part. This is a most important topic for Computers. Computer software consists pf sets of programmed instructions which enable the hardware units to perform. Programming a computer to perform has always been a very difficult task. The first electronic computer was programmed using wired panels. Today’s computers are programmed using software.

 

Computer software can be broadly classified into two categories – System Software and Application Software. System software is a set of instructions to the machine hardware to interpret and execute application software. Application software is a set of programming instructions for specific applications like payroll accounting, inventory control, etc. System software consists of language translators [called compilers (compiles program-wise), interpreters (compiles like-wise) and assemblers (converts semi-machine-language, macro-instructions, to machine language)], operating systems, utilities and special purpose software.

 

Computer software or just software is a general term used to describe a collection of computer programs, procedures and documentation that perform some tasks on a computer system. “Software” is sometimes used in a broader context to mean anything which is not hardware but which is used with hardware, such as film, tapes and records. 

We will discuss on languages translator in next post.

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Input and Output Devices-4

Still today we have discussed for different types of the computer hardware devices. Form last few days we are talking on input and output devices which is most important part of the computer hardware. The input or output units of a computer system establish the communication between the system and its users. A large number of input and output units are available in the market. A few of them are discussed in this note.

Most recent trend for data input is towards source data automation. The equipments used for source data automation capture data as a by-product of a business activity thereby completely eliminating manual input of data. Some examples are:

1. Magnetic ink character recognition devices are used by the banking industry to read the account numbers on cheques directly and do the necessary processing.
2. Optical mark recognition devices can sense marks on computer readable papers.

This king of device is used by academic and testing institutions to grade aptitude tests where candidates mark the correct alternatives on a special sheet of paper. These answer sheets are then directly read by the optical mark recognition devices and the information sent to a computer for processing.

Input and Output Devices-3

We talked about input or output units of a computer system. Input and output establish the communication between the system and its users. A large number of input and output units are available in the market. A few of them we are discussing here. We talked about hard disk in our previous post. Today we are going to talk about printer.

 

A printer is a peripheral which produces a hard copy of documents stored in electronic form, usually on physical print media. Printers are purely output devices. Printers are classified into line printers and dot matrix printers. A line printer prints one line of information simultaneously, whereas a dot matrix printer prints one character at a time. A dot matrix printer uses a 5 X 7 or 7 X 9 dot matrix formation to represent each character. Dot matrix printers therefore provide a broken appearance to the characters, whereas a line printer provides a better quality output. A line printer has a speed of about 2000 lines per minute whereas a dot matrix printer has a lower speed of approximately 100 characters per second. If we talke about credit card printer than they need to have a merchant accounts with which credit card processing done. In big shopping mall credit card machine are available there.  With credit card software  and credit card terminal they use credit card printer  to for day to day functions.

Daisy wheel printers and letter quality printers are also character printers. But they produce excellent quality output. However, they are more expensive and slower than dot matrix printers. All the printers discussed so far are called impact printers as they make physical contact with paper while printing. A no impact printer on the other hand transfers information to paper without any physical contact. Example of no impact printers is laser printers, xerographic printers, electrostatic printers, etc.

 

Many printers are primarily used as local peripherals, and are attached by a printer cable or, in most new printers, a USB cable to a computer which serves as a document source. Some printers, commonly known as network printers, have built-in network interfaces (typically wireless or Ethernet), and can serve as a hardcopy device for any user on the network. Individual printers are often designed to support both local and network connected users at the same time.

Input and Output Devices-2

Terminals have become very popular interactive input and output units. A terminal, when connected to a CPU, sends data and instructions directly into the computer. Terminals can be classified into two types, namely, hard copy terminals and soft copy terminals. A hard copy terminal provides a print out on paper whereas a soft copy terminal provides a visual display on a screen. A soft copy terminal is also known as a CRT (Cathode Ray Tube) terminal.

 

Key-to-tape, key-to-disk and key-to-diskette are stand alone data entry stations. There units usually have a small processor attached to a key board and a visual display unit. The processor checks for the accuracy of data at the time of entry. The screen displays what is being entered. There facilities are highly desirable for a data processing centre. Hence most of the data processing centres are switching over from punched card input to data entry stations.

 

A graphic display terminal displays information in both character and graphic forms. These are extensively used for CAD/CAM (computer aided design/computer aided manufacture) applications.

A potter is used to obtain printed copies of graphic outputs. It is used by architects and designers to produce blueprints of their design on paper.

Input and Output Devices-1

Still today we have already discussed different computer hardware parts. In our last talk we have discussed on magnetic disk. The Diskettes and Winchester disks provide random access memory on micro-computers. A diskette is a smaller disk of 5¼ inch in diameter. It provides a storage capacity of 360 KB and an average access time of 180 milli seconds. Today we are going to discuss one other and important part of computer hardware and that is input and Output devices.  

 

Input and Output Devices 

The input or output units of a computer system establish the communication between the system and its users. A large number of input and output units are available in the market. A few of them are discussed in this note.

 

Punched card is the most ancient (few decades old) input medium. Instruction and data punched on cards are transmitted into a computer through a card reader. A printed card had survived a whole century because of its simplicity. But it is on its way out now. Punched cards are being replaced by terminals which provide direct data entry. In next post we will discuss briefly on input and output devices.

 

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Magnetic Disk-2

Each recording surface is divided into a series of concentric circles called tracks and each track is further divided into sectors. The capacity of each sector whether it is on the inner most track or outer most track is a constant. One important characteristic of a disk drive is the access time which represents the time needed to access the desired record from a disk. Access time consists of two components, namely, seek time and rotational delay. Seek time represents the time required to seek the desired track on the desired recording surface. This involves a movement of the access arm, which supports the read/write head. Rotational delay represents the time required for the rotating disk to position the desired sector under the read/write head. Access times of 35 milli seconds are common. Disk packs are classified into three types, namely, removable disks, fixed disks and Winchester disks. 

A removable disk pack, as the name indicates, can be transported and replaced. A fixed disk pack on the other hand, cannot be removed or transported or replaced. However, it provides a quicker access time. A disk storage capacity of 600-1000 MB is very common. Winchester disks are a special type of hard disks and are supported mainly by micro-computers. A Winchester disk provides a storage capacity in the range of 10 MB – 80 MB.

EVOLUTION OF COMPUTER-2

The first commercial computer called Univac (Universal Automatic Computer) using vacuum tube circuits was used by the U.S. Census Bureau in 1951. Computers using vacuum tube circuits belonged to FERST GENRATION COMPUTERS. Invention of the transistor by Bell Labs in U.S.A. gave birth to Second Generation Computers which used transistors instead of vacuum tubes. An example of Second Generation Computer is the IBM 1401. Third Generation Computers were introduced in the mid-1960 with the invention of tiny integrated circuits on silicon chips. IBM released its 360 series computers with integrated chips of 28/1000 each sq. carrying more than 1000 circuits. Large scale integrated chips become available in1969. Computers which used large scale integrated chips can be called Forth Generation Computers even though there is no general agreement on what constitutes a Forth Generation Computer.

 

Invention of the micro-processor in 1972 has changed the computing scene dramatically. A micro-processor when interfaced with memory and input/output units become a micro computer. A micro-computer is very small in size (can be actually placed on a table top) but is very powerful and provides a user-friendly atmosphere for managers to interact with it. The first business micro-computer called APPLE II was released in U.S.A. in 1977. A micro-computer which is reasonably powerful can be bought today for as low as Rs.20,000.

 

Recent advances in the field of artificial intelligence are being used to design a “thinking computer”. These computers can be called Fifth Generation Computers. A special feature anticipated in this computers is their ability to respond to spoken words. These computers are expected to be in the market by 1990.

EVOLUTION OF COMPUTER-1

Computers have brought about a revolution in the field of computing as a result of technological advancement in the field of electronics. “Abacus”, the fist mathematical device used to facilitate arithmetical computation, was invented by the ancient Chinese before the birth of Christ. Abacus beads Strung of wires to aid arithmetical computations and is believed to have been in use till recently. 

The first mechanical ‘Computer’ called ‘Analytical Engine’ designed by Charles

Babbage between 1830 and 1850 marked the birth of computer age. This was the first mechanical computer capable of performing basic arithmetical functions. Charles Babbage designed his analytical engine around five components, namely,

 

• A STORE to hold numbers,
• An ARITHMETIC UNIT (which he called the ‘Mill’) to perform arithmetical operations,
• A CONTROL UNIT to control and coordinate various activities in the correct sequence,
• An IMPUT device to transfer both numbers and instructions into the computer, and
• An OUTPUT device to display the results of computations.

Remarkably even today’s computers are built around the same concepts. However, modern electronic computers provide three major advantages:

 

• Enabling the computer to operate at electronic speeds (an electron travels approximately 1 foot in 1 billionth of a seconds),
• Providing tremendous reliability,
• Making the computer a general purpose machine.

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