There are three main types of computers based on their principles of operation: analog computers, digital computers, and hybrid computers. Digital computers are the most common today and operate using binary numbers. Computers can also be classified based on their size, memory capacity, and processing speed into supercomputers, mainframe computers, mini computers, and microcomputers (personal computers). Microcomputers are the most ubiquitous. Computers also have different functions and configurations including servers, workstations, information appliances, and embedded systems. Buses and ports allow for communication between different computer components. A modem facilitates data transmission over telephone or cable lines by converting between digital and analog formats.

1. Hina Anjum
CLASSIFICATION OF COMPUTERS

2. CLASSIFICATION OF COMPUTERS
A computer is a machine that can be programmed to manipulate symbols. Its principal
characteristics 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 three
types of computers are:

3. Analog Computers
Analog Computer is a computing device that works on continuous range of values. The results
given by the analog computers will only be approximate since they deal with quantities that vary
continuously. It generally deals with physical variables such as voltage, pressure, temperature,
speed, etc.
Digital Computers
On the other hand a digital computer operates on digital data such as numbers. It uses binary
number 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 input
or output signal. These two levels are known as logic 0 and logic 1. Digital Computers can give
more accurate and faster results. Digital computer is well suited for solving complex problems in
engineering and technology. Hence digital computers have an increasing use in the field of
design, research and data processing.

4. Based on the purpose, Digital computers can be further classified as,
General Purpose Computers
Special Purpose Computers
Special purpose computer is one that is built for a specific application. General purpose
computers are used for any type of applications. They can store different programs and do the
jobs as per the instructions specified on those programs. Most of the computers that we see today
are general purpose computers.
Hybrid Computers
A hybrid computer combines the desirable features of analog and digital computers. It is mostly
used for automatic operations of complicated physical processes and machines. Now-a-days
analog-to-digital and digital-to-analog converters are used for transforming the data into suitable
form for either type of computation.
For example, in hospital’s ICU, analog devices might measure the patient’s temperature, blood
pressure and other vital signs. These measurements which are in analog might then be converted

5. into numbers and supplied to digital components in the system. These components are used to
monitor the patient’s vital sign and send signals if any abnormal readings are detected. Hybrid
computers 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 performance
and capacity. The four types are:
Super Computers
When we talk about types of computers, the first type that comes to our mind would be Super
computers. 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.

6. Mainframe Computers
Mainframe computers can also process data at very high speeds, hundreds of million instructions
per second and they are also quite expensive. Normally, they are used in banking, airlines and
railways 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 Computers
Mini computers are lower to mainframe computers in terms of speed and storage capacity. They
are also less expensive than mainframe computers. Some of the features of mainframes will not

7. be available in mini computers. Hence, their performance also will be less than that of
mainframes.
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 Computers
The invention of microprocessor (single chip CPU) gave birth to the much cheaper micro
computers. 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.

8. They are further classified into:
Tower Model
The term refers to a computer in which the power supply, motherboard, and mass storage devices
are stacked on top of each other in a cabinet. This is in contrast to desktop models, in which
these components are housed in a more compact box. The main advantage of tower models is
that there are fewer space constraints, which makes installation of additional storage devices
easier.
Desktop Model
A computer designed to fit comfortably on top of a desk, typically with the monitor sitting on top
of the computer. Desktop model computers are broad and low, whereas tower model computers
are narrow and tall. Because of their shape, desktop model computers are generally limited to
three internal mass storage devices. Desktop models designed to be very small are sometimes
referred to as slim line models.

9. Notebook Computer
A light weighted personal computer. Notebook computers typically weigh less than 6 pounds and
are small enough to fit easily in a briefcase. Aside from size, the principal difference between a
notebook computer and a personal computer is the display screen. Notebook computers use a
variety of techniques, known as flat-panel technologies, to produce a lightweight and non-bulky
display screen. The quality of notebook display screens varies considerably. In terms of
computing 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 small
package is expensive. Notebook computers cost about twice as much as equivalent regular-sized
computers. Notebook computers come with battery packs that enable you to run them without
plugging them in. However, the batteries need to be recharged every few hours.
Laptop Computer
A small, portable computer. Nowadays, laptop computers are more frequently called notebook
computers.

10. Subnotebook Computer
A 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 otherwise
equivalent to notebook computers.
Hand-held Computer
A portable computer that is small enough to be held in one’s hand. Although extremely
convenient to carry, handheld computers have not replaced notebook computers because of their
small keyboards and screens. The most popular hand-held computers are those that are
specifically designed to provide PIM (personal information manager) functions, such as a
calendar and address book. Some manufacturers are trying to solve the small keyboard problem
by replacing the keyboard with an electronic pen. However, these pen-based devices rely on
handwriting recognition technologies, which are still in their infancy. Hand-held computers are
also called PDAs, palmtops and pocket computers.
Palmtop
A small computer that literally fits in your palm. Compared to full-size computers, palmtops are
severely limited, but they are practical for certain functions such as phone books and calendars.

11. Palmtops that use a pen rather than a keyboard for input are often called hand-held computers or
PDAs. 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 other
devices. Palmtops are also called PDAs, hand-held computers and pocket computers.
PDA
Short 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, and
personal organizer. Unlike portable computers, most PDAs are pen-based, using a stylus rather
than a keyboard for input. This means that they also incorporate handwriting recognition
features. Some PDAs can also react to voice input by using voice recognition technologies. The
field of PDA was pioneered by Apple Computer, which introduced the Newton MessagePad in
1993. Shortly thereafter, several other manufacturers offered similar products. To date, PDAs
have had only modest success in the marketplace, due to their high price tags and limited
applications. However, many experts believe that PDAs will eventually become common
gadgets.
PDAs are also called palmtops, hand-held computers and pocket computers.
Types of Computers based on Functions:
Servers

12. Server usually refers to a computer that is dedicated to provide a service. For example, a
computer dedicated to a database may be called a "database server". "File servers" manage a
large collection of computer files. "Web servers" process web pages and web applications. Many
smaller servers are actually personal computers that have been dedicated to provide services for
other computers.
Workstations
Workstations are computers that are intended to serve one user and may contain special hardware
enhancements not found on a personal computer.
Information Appliances
Information appliances are computers specially designed to perform a specific user-
friendly function —such as playing music, photography, or editing text. The term is most
commonly applied to mobile devices, though there are also portable and desktop devices of this
class.

13. Embedded Computers
Embedded computers are computers that are a part of a machine or device. Embedded computers
generally execute a program that is stored in non-volatile memory and is only intended to operate
a specific machine or device. Embedded computers are very common. Embedded computers are
typically required to operate continuously without being reset or rebooted, and once employed in
their task the software usually cannot be modified. An automobile may contain a number of
embedded 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 for
the computational requirements of the specific application and may be slower and cheaper than
CPUs found in a personal computer.
BUS

14. A bus, in computing, is a set of physical connections (cables, printed circuits, etc.) which can be
shared 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 between
the components, by carrying out all communications over a single data channel. This is why the
metaphor of a "data highway" is sometimes used.
Characteristics of a bus
A bus is characterized by the amount of information that can be transmitted at once. This
amount, expressed in bits, corresponds to the number of physical lines over which data is sent
simultaneously. A 32-wire ribbon cable can transmit 32 bits in parallel. The term "width" is used
to 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 of
data 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 data
which it can transport per unit of time, by multiplying its width by its frequency. A bus with a
width 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/s
Or 266*106 /1000 = 266*103 KB/s
Or 259.7*103 /1000 = 266 MB/s
Bus Subassembly

15. In reality, each bus is generally constituted of 50 to 100 distinct physical lines, divided into three
subassemblies:
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 Buses
There 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 system's central memory (the RAM).

16. 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.
PORTS
In computer networking a port is an application-specific or process-specific software construct
serving as a communications endpoint in a computer's host operating system. A port is associated
with an IP address of the host, as well as the type of protocol used for communication. In plain
English, the purpose of ports is to uniquely identify different applications or processes running
on 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 as
the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) of the Internet
Protocol Suite. A port is identified for each address and protocol by a 16-bit number, commonly
known as the port
Note that it is the combination of IP address and port number together that must be globally
unique. Thus, different IP addresses or protocols may use the same port number for
communication; 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 same
number.

17. Types of Ports:
Ethernet
Ethernet port
IEEE 1394 interface
IEEE 1394 interface
Parallel
Parallel port
PS/2
PS/2 connector

18. Serial
Serial port
USB
USB
VGA
VGA connector
Digital Visual Interface
Digital Visual Interface

19. SCSI
SCSI
MODEM
Short for modulator-demodulator. A modem is a device or program that enables a computer to
transmit data over, for example, telephone or cable lines. Computer information
is stored digitally, whereas information transmitted over telephone lines is transmitted in the
form of analog waves. A modem converts between these two forms.
Fortunately, there is one standard interface for connecting external modems to computers
called RS-232. Consequently, any external modem can be attached to any computer that has an
RS-232 port, which almost all personal computers have. There are also modems that come as
a board that you can insert into a vacant expansion slot. These are sometimes called
onboard or internal modems.
While the modem interfaces are standardized, a number of different protocols for formatting data
to be transmitted over telephone lines exist. Some, like CCITT V.34, are official standards, while
others have been developed by private companies. Most modems have built-in support for the
more common protocols -- at slow data transmission speeds at least, most modems can
communicate with each other. At high transmission speeds, however, the protocols are less
standardized.