CLASSIFICATION OF COMPUTERSA computer is a machine that can be programmed to manipulate symbols. Its principalcharacteristics are: § It responds to a specific set of instructions in a well-defined manner. § It can execute a prerecorded list of instructions (a program). § It can quickly store and retrieve large amounts of data. Computers can be classified in various ways depending upon its size, memory capacity,processing speed etc.Types of Computers based on Principles of Operation:There are three different types of computers according to the principles of operation. Those threetypes of computers are:
Analog ComputersAnalog Computer is a computing device that works on continuous range of values. The resultsgiven by the analog computers will only be approximate since they deal with quantities that varycontinuously. It generally deals with physical variables such as voltage, pressure, temperature,speed, etc.Digital ComputersOn the other hand a digital computer operates on digital data such as numbers. It uses binarynumber system in which there are only two digits 0 and 1. Each one is called a bit.The digital computer is designed using digital circuits in which there are two levels for an inputor output signal. These two levels are known as logic 0 and logic 1. Digital Computers can givemore accurate and faster results. Digital computer is well suited for solving complex problems inengineering and technology. Hence digital computers have an increasing use in the field ofdesign, research and data processing.
Based on the purpose, Digital computers can be further classified as, General Purpose Computers Special Purpose ComputersSpecial purpose computer is one that is built for a specific application. General purposecomputers are used for any type of applications. They can store different programs and do thejobs as per the instructions specified on those programs. Most of the computers that we see todayare general purpose computers.Hybrid ComputersA hybrid computer combines the desirable features of analog and digital computers. It is mostlyused for automatic operations of complicated physical processes and machines. Now-a-daysanalog-to-digital and digital-to-analog converters are used for transforming the data into suitableform for either type of computation.For example, in hospital’s ICU, analog devices might measure the patient’s temperature, bloodpressure and other vital signs. These measurements which are in analog might then be converted
into numbers and supplied to digital components in the system. These components are used tomonitor the patient’s vital sign and send signals if any abnormal readings are detected. Hybridcomputers are mainly used for specialized tasks.Types of Computers based on Configuration:There are four different types of computers when we classify them based on their performanceand capacity. The four types are:Super ComputersWhen we talk about types of computers, the first type that comes to our mind would be Supercomputers. They are the best in terms of processing capacity and also the most expensive ones.These computers can process billions of instructions per second. They are huge computers installed in space centers, nuclear power stations etc. They are used for performing complex mathematical calculations. Only scientists and mathematicians can operate them. They are having huge memories & tremendous processing speed. They are used for weather forecasting, animation graphics etc.
Mainframe ComputersMainframe computers can also process data at very high speeds, hundreds of million instructionsper second and they are also quite expensive. Normally, they are used in banking, airlines andrailways etc for their applications. They are big computer systems sensitive to temperature, humidity, dust etc. Qualified & trained operators are required to operate them. They have wide range of peripherals attached. They have large storage capacity. They can use wide variety of software. They are not user friendly. They can be used for more mathematical calculations. They are installed in large commercial places or government organizations.Mini ComputersMini computers are lower to mainframe computers in terms of speed and storage capacity. Theyare also less expensive than mainframe computers. Some of the features of mainframes will not
be available in mini computers. Hence, their performance also will be less than that ofmainframes. They have less memory & storage capacity than mainframe computers. They offer limited range of peripherals. Limited range of software can be used by them. The end users can directly operate it. They are not very sensitive to the external environment and hence are more generalized. They are used for data processing.Micro ComputersThe invention of microprocessor (single chip CPU) gave birth to the much cheaper microcomputers. Microcomputers are the most common type of computers used by people today,whether in a workplace, at school or on the desk at home. They brought revolution in the history of computers. They are also known as Personal Computers. They are cheap and user friendly. The main components are Monitor, CPU, Keyboard, Mouse, Speakers, Modem and Printer. They are having limited peripherals attached to them. This type of computers can use wide range of software. They are used as desktops either in offices or even homes. Their operation can be easily learnt by anyone having logical aptitude. Children enjoy playing games & watching movies in these computers. Most popular micro computer’s processing chip manufacturing company is Intel.
They are further classified into:Tower ModelThe term refers to a computer in which the power supply, motherboard, and mass storage devicesare stacked on top of each other in a cabinet. This is in contrast to desktop models, in whichthese components are housed in a more compact box. The main advantage of tower models isthat there are fewer space constraints, which makes installation of additional storage deviceseasier.Desktop ModelA computer designed to fit comfortably on top of a desk, typically with the monitor sitting on topof the computer. Desktop model computers are broad and low, whereas tower model computersare narrow and tall. Because of their shape, desktop model computers are generally limited tothree internal mass storage devices. Desktop models designed to be very small are sometimesreferred to as slim line models.
Notebook ComputerA light weighted personal computer. Notebook computers typically weigh less than 6 pounds andare small enough to fit easily in a briefcase. Aside from size, the principal difference between anotebook computer and a personal computer is the display screen. Notebook computers use avariety of techniques, known as flat-panel technologies, to produce a lightweight and non-bulkydisplay screen. The quality of notebook display screens varies considerably. In terms ofcomputing power, modern notebook computers are nearly equivalent to personal computers.They have the same CPUs, memory capacity, and disk drives. However, all this power in a smallpackage is expensive. Notebook computers cost about twice as much as equivalent regular-sizedcomputers. Notebook computers come with battery packs that enable you to run them withoutplugging them in. However, the batteries need to be recharged every few hours.Laptop ComputerA small, portable computer. Nowadays, laptop computers are more frequently called notebookcomputers.
Subnotebook ComputerA portable computer that is slightly lighter and smaller than a full-sized notebook computer.Typically, subnotebook computers have a smaller keyboard and screen, but are otherwiseequivalent to notebook computers.Hand-held ComputerA portable computer that is small enough to be held in one’s hand. Although extremelyconvenient to carry, handheld computers have not replaced notebook computers because of theirsmall keyboards and screens. The most popular hand-held computers are those that arespecifically designed to provide PIM (personal information manager) functions, such as acalendar and address book. Some manufacturers are trying to solve the small keyboard problemby replacing the keyboard with an electronic pen. However, these pen-based devices rely onhandwriting recognition technologies, which are still in their infancy. Hand-held computers arealso called PDAs, palmtops and pocket computers.PalmtopA small computer that literally fits in your palm. Compared to full-size computers, palmtops areseverely limited, but they are practical for certain functions such as phone books and calendars.
Palmtops that use a pen rather than a keyboard for input are often called hand-held computers orPDAs. Because of their small size, most palmtop computers do not include disk drives. However,many contain PCMCIA slots in which you can insert disk drives, modems, memory, and otherdevices. Palmtops are also called PDAs, hand-held computers and pocket computers.PDAShort for personal digital assistant, a handheld device that combines computing, telephone/fax,and networking features. A typical PDA can function as a cellular phone, fax sender, andpersonal organizer. Unlike portable computers, most PDAs are pen-based, using a stylus ratherthan a keyboard for input. This means that they also incorporate handwriting recognitionfeatures. Some PDAs can also react to voice input by using voice recognition technologies. Thefield of PDA was pioneered by Apple Computer, which introduced the Newton MessagePad in1993. Shortly thereafter, several other manufacturers offered similar products. To date, PDAshave had only modest success in the marketplace, due to their high price tags and limitedapplications. However, many experts believe that PDAs will eventually become commongadgets.PDAs are also called palmtops, hand-held computers and pocket computers.Types of Computers based on Functions:Servers
Server usually refers to a computer that is dedicated to provide a service. For example, acomputer dedicated to a database may be called a "database server". "File servers" manage alarge collection of computer files. "Web servers" process web pages and web applications. Manysmaller servers are actually personal computers that have been dedicated to provide services forother computers.WorkstationsWorkstations are computers that are intended to serve one user and may contain special hardwareenhancements not found on a personal computer.Information AppliancesInformation appliances are computers specially designed to perform a specific user-friendly function —such as playing music, photography, or editing text. The term is mostcommonly applied to mobile devices, though there are also portable and desktop devices of thisclass.
Embedded ComputersEmbedded computers are computers that are a part of a machine or device. Embedded computersgenerally execute a program that is stored in non-volatile memory and is only intended to operatea specific machine or device. Embedded computers are very common. Embedded computers aretypically required to operate continuously without being reset or rebooted, and once employed intheir task the software usually cannot be modified. An automobile may contain a number ofembedded computers; however, a washing machine and a DVD player would contain only one.The central processing units (CPUs) used in embedded computers are often sufficient only forthe computational requirements of the specific application and may be slower and cheaper thanCPUs found in a personal computer. BUS
A bus, in computing, is a set of physical connections (cables, printed circuits, etc.) which can beshared by multiple hardware components in order to communicate with one another.The purpose of buses is to reduce the number of "pathways" needed for communication betweenthe components, by carrying out all communications over a single data channel. This is why themetaphor of a "data highway" is sometimes used.Characteristics of a busA bus is characterized by the amount of information that can be transmitted at once. Thisamount, expressed in bits, corresponds to the number of physical lines over which data is sentsimultaneously. A 32-wire ribbon cable can transmit 32 bits in parallel. The term "width" is usedto refer to the number of bits that a bus can transmit at once.Additionally, the bus speed is also defined by its frequency (expressed in Hertz), the number ofdata packets sent or received per second. Each time that data is sent or received is called a cycle.This way, it is possible to find the maximum transfer speed of the bus, the amount of datawhich it can transport per unit of time, by multiplying its width by its frequency. A bus with awidth of 16 bits and a frequency of 133 MHz, therefore, has a transfer speed equal to:16 * 133.106 = 2128*106 bit/s,Or 2128*106/8 = 266*106 bytes/sOr 266*106 /1000 = 266*103 KB/sOr 259.7*103 /1000 = 266 MB/sBus Subassembly
In reality, each bus is generally constituted of 50 to 100 distinct physical lines, divided into threesubassemblies: The address bus (sometimes called the memory bus) transports memory addresses which the processor wants to access in order to read or write data. It is a unidirectional bus. The data bus transfers instructions coming from or going to the processor. It is a bidirectional bus. The control bus (or command bus) transports orders and synchronization signals coming from the control unit and travelling to all other hardware components. It is a bidirectional bus, as it also transmits response signals from the hardware.Primary BusesThere are generally two buses within a computer: Internal bus (sometimes called the front-side bus or FSB for short). The internal bus allows the processor to communicate with the systems central memory (the RAM).
Expansion bus (sometimes called the input/output bus) allows various motherboard components (USB, serial, and parallel ports, cards inserted in PCI connectors, hard drives, CD-ROM and CD-RW drives, etc.) to communicate with one another. However, it is mainly used to add new devices using what are called expansion slots connected to the input/output bus. PORTSIn computer networking a port is an application-specific or process-specific software constructserving as a communications endpoint in a computers host operating system. A port is associatedwith an IP address of the host, as well as the type of protocol used for communication. In plainEnglish, the purpose of ports is to uniquely identify different applications or processes runningon a single computer and thereby enable them to share a single physical connection to a packet-switched network like the Internet.The protocols that primarily use ports are the Transport Layer protocols, such asthe Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) of the InternetProtocol Suite. A port is identified for each address and protocol by a 16-bit number, commonlyknown as the portNote that it is the combination of IP address and port number together that must be globallyunique. Thus, different IP addresses or protocols may use the same port number forcommunication; e.g., on a given host or interface UDP and TCP may use the same port number,or on a host with two interfaces, both addresses may be associated with a port having the samenumber.
Serial Serial portUSB USBVGA VGA connectorDigital Visual Interface Digital Visual Interface
SCSI SCSI MODEMShort for modulator-demodulator. A modem is a device or program that enables a computer totransmit data over, for example, telephone or cable lines. Computer informationis stored digitally, whereas information transmitted over telephone lines is transmitted in theform of analog waves. A modem converts between these two forms.Fortunately, there is one standard interface for connecting external modems to computerscalled RS-232. Consequently, any external modem can be attached to any computer that has anRS-232 port, which almost all personal computers have. There are also modems that come asa board that you can insert into a vacant expansion slot. These are sometimes calledonboard or internal modems.While the modem interfaces are standardized, a number of different protocols for formatting datato be transmitted over telephone lines exist. Some, like CCITT V.34, are official standards, whileothers have been developed by private companies. Most modems have built-in support for themore common protocols -- at slow data transmission speeds at least, most modems cancommunicate with each other. At high transmission speeds, however, the protocols are lessstandardized.