PERSONAL COMPUTERS (PC)

These microcomputers are single user system and are used for a variety of purposes, such as payroll, business accounts, word processing, legal and medical record keeping, accessing  Internet resources (email, Web search). They are also known as personal computers (PC). Typically the price ranges from $500-$5000 for a single user system. E.g- IBM Personal Computers (Aptiva series), The HP Pavilion series, Apple Macintosh series, DELL series, etc.
       A typical configuration of the microcomputer spectrum includes a 32/64 bit microprocessor, 256MB-1GB of system memory (RAM), a monitor, a hard disk with storage capacity more than 80 GB, a CD-ROM drive, and a 31/2" high density floppy disk drive, etc.

Microcomputers

The 4-bit and 8-bit microprocessors became available in the mid-1970s, and initial applications were primarily in the areas of machine control and instrumentation. As the price of the microprocessors and memory began to decline, the applications mushroomed in almost all areas, such as video games, word processing, and small-business applications.early microcomputers were designed around 8 bit microprocessors. Since then 16, 32, 64 bits microprocessors, such as Intel 8086/88, Pentium I to IV, Motorola 68000, and the power PC series have been introduced, and recent micro computers are designed around these microprocessors. Present day micro computers can be classified in 4 groups: personal (or business) computers (PC), work stations, single board, and single chip microcomputers (microcontrollers).

Large Computers

These are large, general purpose, multiuser, multitasking, computers designed to perform such data processing tasks as complex scientific and engineering calculations,and handling of records for large corporations or government agencies. These computers can be broadly classified into mainframes and supercomputers, and mainframes are further classified according to their sizes. the prices ranges from $100,000 to millions of dollars. Typical examples are IBM System/390 series, Cray computers (Cray-2, Y-MP), the Fujitsu GS8800, and the Hitachi MP5800.
   Mainframes are high-speed computers, and their word length generally ranges from 32 to 64 bits. They are capable of addressing megabytes of memory and handling all types of peripherals and a large number of users. Supercomputers such as the Cray-2 and Y-MP are 64 bits high performance and high-speed computers. They  are the fastest computers, capable of executing billions of instructions per second, and are used primarily  in research dealing with problems in areas such as global climate and high-energy physics.

                                                               Fig: A mainframe computer

Introduction

Since 1950, advances in semiconductor technology have had an unprecedented impact on computers. In the 1960s, computers were accessible only to big corporations, universities, and government agencies. Now "computer" has become a common word. The range of computers now available extends from such sophisticated, multimillion dollar machines as the Cray computers to the less-than-$1000 personal computers.
      Different types of computers are designed to serve different purposes. Some are suitable for scientific calculations, while others are used simply for tuning appliances on and off. Until the 1970s computers were broadly classified in three categories: mainframe, mini, and micro computers. Since then technology has changed considerably, and the distinction between the categories have been blurred. Initially the micro computer was recognized as the computer with a microprocessor as its CPU.