1.4 COMPUTER SYSTEM
Each computer consists of a series of devices that together operate as an integrated unit or
computer system. The processor is made up of the memory, arithmetic, logic and control
units. A large computer system will normally have one or more auxiliary units, where
input and output data are stored. A brief description of computer system is given here.
More detailed study about this will be covered in unit 2 in this block.
1.4.1 How Computers Work ?
Input: This is the process of entering data and programs in to the computer system. Since
computer is an electronic machine like any other machine which takes as inputs raw data
and performs some processing giving out processed data, the input unit takes data from
user to the computer in an organized manner for processing. Information and programs
are entered into the computer through input devices such as the keyboard, disks, or
through other computers via network connections or modems connected to the internet.
Storage: The process of saving data and instructions permanently is known as storage.
Data has to be fed into the system before the actual processing starts. It is because the
processing speed of Central Processing Unit (CPU) is so fast that the data has to be
provided to CPU with the same speed. Therefore the data is first stored in the storage unit
for faster access and processing. This storage unit or the primary storage of the computer
system is designed to do the above functionality. It provides space for storing data and
instructions. The storage unit performs the following major functions:
(A) All data and instructions are stored here before and after processing.
(B) Intermediate results of processing are also stored here.
(B) Intermediate results of processing are also stored here.
Processing: The task of performing operations like arithmetic and logical operations is
called processing. The CPU or central processing unit takes data and instructions from
the storage unit and makes all sorts of calculations based on the instructions given and the
type of data provided. It is then sent back to the storage unit. The coprocessor or the
arithmetic-logic unit does arithmetic and logical operations. The RAM temporarily stores
information.
Output: This is the process of producing results from the data for getting useful
information. Output devices display information on the screen (monitor) or the printer
and sends information to other computers. They also display messages about what errors
may have occurred and brings up message or dialog box asking for more information to
be input. Again the output is also stored inside the computer for further processing.
1.4.2 Operational Unit
In order to carry out the operations, the computer allocates the task among its various
operational units. These are 1) arithmetic logical unit, 2) control unit, and 3) central
processing unit.
Arithmetic Logical Unit (ALU)
The Arithmetic Logical Unit is an important component of the CPU, which carry the
actual execution of the instructions. After entering the data through the input device it is stored in the primary storage unit. Then processing of the data and instruction are
performed by Arithmetic Logical Unit. The major operations performed by the ALU are
addition, subtraction, multiplication, division, logic and comparison. Data is transferred
to ALU from storage unit when required. After processing, the output is returned to the
storage unit for further processing or getting stored.
Control Unit (CU)
The next component of computer is the Control Unit, which acts like the supervisor
seeing that things are done in proper fashion. The control unit determines the sequence in
which computer programs and instructions are executed. Things like processing of
programs stored in the main memory, interpretation of the instructions and issuing of
signals for other units of the computer to execute them. It also acts as a switch board
operator when several users access the computer simultaneously. Thereby it coordinates
the activities of computer‟s peripheral equipment as they perform the input and output.
Therefore, it is the manager of all operations mentioned in the previous section.
Central Processing Unit (CPU)
1.4.3 System Unit
A computer system unit contains many parts :
Ports and Connectors : A port is a connector located on the motherboard or on a
separate adapter. Ports and Connectors allow the computer to communicate with different
devices and peripherals attached with it.
Power Supply : Power supply changes normal household electricity into electricity that a computer can use. A power supply or power supply unit (PSU) is an internal component used to supply the power to the components of a computer. Power supply is rated by the number of watts it generates.
1.4.4 Von Neumann Architecture
Mathematician John
Von Neumann
conceived a
computer
architecture which
forms the core of
nearly every
computer system in
use today
Mathematician John Von Neumann conceived a computer architecture which forms the
core of nearly every computer system in use today. This architecture is known as Von
Neumann architecture. It is a design model for the modern computers which has central
processing unit (CPU) and the concept of memory used for storing both data and
instructions. This model implements the stored program concept in which the data and
the instructions both are stored in the memory. All computers share the same basic
architecture which have memory, an I/O system, arithmetic logic unit (ALU) and control
unit (CU).
1.4.5 Classification of Computers
Computers are available in different sizes, shapes, and weights. Due to these different
sizes and shapes, they perform different sort of jobs from one another. They can be
classified in different ways. All the computers are designed by qualified computer
architects who design these machines as per different requirements. A computer that is
used in a home differs in size and shape from the computer being used in a hospital.
Following sections are going to describe different classifications of computers. The term
“capacity” refers to the volume of work or the data processing capacity a computer can
handle. Their performance is judged by the:
1. Amount of data that can be stored in memory
2. Speed of internal operation of the computer
3. Number and type of peripheral devices
4. Amount and type of software available for use with the computer
The capacity of early generation computers were determined by their physical size- the
large the size, the greater the volume. In computer terms, size and speed of operation are
at present proportionate to each other. Generally, though, recent, technology is tending to
create smaller machines, making it possible to package equivalent speed and capacity in a
smaller format.
Microcomputers: The mass production of silicon chips since 1971 has made it possible
to put a “brain” into all sorts of machines. One such machine is the microcomputer. This
machine has taken fullest advantage of the use of large-scale integration on silicon chips.
The microprocessors literally contain a computer on a chip that can pass through the eye
of needle. Microcomputers memories are generally made of semiconductors fabricated on
silicon‟s chips. It is a digital computer system under the control of a stored program that
uses a microprocessor, a programmable read-only memory (ROM), and a random-access
memory (RAM). The ROM defines the instructions to be executed by the computer while
RAM is the functional equivalent of computer memory. Today microcomputers are called
as Personal Computers more commonly as PCs. These are small, relatively inexpensive
computers designed for personal use in home or offices.
Minicomputers: Technological advances in the 1960's enabled manufactures to respond
to the growing demand for a similar stand-alone machine, the minicomputer, to handle
task that large computers could not perform economically. Minicomputer systems (or
small mainframe computers) provide faster operating speeds and larger storage capacities
than microcomputers systems. These Computers can support a large number of highspeed input/output devices. Several desk drives can be used to provide online access to
large data files as required for direct - access processing. Operating system developed for
minicomputer systems generally support both multiprogramming and virtual storage.
This means that many programs can be run concurrently. This type of computer system is
very flexible and can be improvised to meet the needs of users. Although the
minicomputer is not as powerful as the medium or large-size computer, it is quite close.
Medium-size Computers : It provides faster operating speeds and larger storage
capabilities than small computer systems. These Computers can support a large number
of high-speed input-output devices, and several disk drives can be used to provide online
access processing. The possibility of increasing the data processing capability of a
computer by adding devices, such additional memory, and other peripheral devices, is
called expandability.
Large Computers : These Computers are the ultimate in flexibility and speed. These
usually contain full control systems with minimal operator intervention. Large computer
systems range from single-processing configurations to nationwide computer based
networks involving general large computers. Large computers have internal operating
speeds measured in terms of nanoseconds, as a compared to smaller computers where
speed in terms of microseconds.
Mainframe Computers : Mainframes are huge, multi-user systems designed to process
millions of instructions per second and capable of accessing billions of data. They can
handle gigantic processing jobs in large corporations or government agencies. This
computer is commonly used in big hospitals, air line reservations companies and many
other huge companies prefer mainframe because of its capability of retrieving data on
huge basis. Mainframe allows its user to maintain large information storage at a
centralized location and be able to access and process this data from different computers
located at different locations.
Mainframe computers are normally too expensive and out of reach from a salaried
person who wants this computer for his home. Mainframe is the second largest in
capability and size of computer family.
Supercomputers : The most expensive in price, biggest and fastest machines today are
the supercomputers that are used when billions or even trillions of calculations are
needed. Supercomputers are ultra fast computers designed to process huge amounts of
scientific data then display the underlying patterns that have been discovered. These
machines are essential for applications ranging from nuclear weapon to accurate weather
forecasting. Super Computers are used for highly calculation-intensive tasks such as
molecular modeling, climate research, weather forecasting, quantum physics, physical
simulations etc.
"They are used for
highly calculationintensive tasks
such as molecular
modeling, climate
research, weather
forecasting,
quantum physics,
physical
simulations etc. "
Supercomputers are machines that have speed in the 100-million-instructions-per-second
range. Governments specially use this type of computer for their different calculations
and heavy duty. Different industries also use this huge computer for designing their
products. It is also used for animation purpose. The PARAM supercomputer is one of the
supercomputer developed by India‟s Center for Development of Advanced
Computing(C-DAC) and promises processing speeds of up to 1 trillions instructions per
second. Since October 2010, the Tianhe-1A supercomputer is considered as the fastest
supercomputer in the world which is located in China. Some of the examples of
Supercomputer are: IBM Blue Gene/L, IBM Roadrunner, Cray Jaguar etc.
1.4.6 Classification by Technology
There are essentially two different types of computer processing. Each is made possible
by a different kind of circuitry, and each is suitable for different purposes.
Analog Computers: The name analog comes from the word “analogous”, meaning
similar. Analog signal is a continuous signal whose amplitude can take any value in a
continuous range. It can have infinite number of values. Analog computers deal with
quantities that are continuously variable. They give only approximate results. These types
of computer provide an analog or simulation of the object or system it represents. It is
especially useful for solving problems that involve relationships between variable
quantities in systems that change with time. The analog compute may express changing
relationships in output in the form of graphs. It is able to create such pictures because it
responds to changes in electrical voltages that match changes in variable quantities.
Digital Computers : It is a machine that specializes in counting. It operates by counting values that are discrete, or separate and distinct, unlike the continuous quantities that can be measured by the analog computer. Digital signal is a discrete time signal that has a discrete number of levels. It can only assume one of the two values 0 or 1. While analog technology uses continuous signals, digital technology encodes the information into discrete signal states. Digital Computers are used for both business data processing and accuracy. The basic operation performed by a digital computer is addition. It can store the sums of addition problems as they accumulate, and can complete a single calculation in a fraction of a nanosecond. The digital computer is capable of storing data as long as needed, performing logical operations, editing input data, and printing out the results of its processing at high speed. Advantages of digital systems include flexible processing, easy to design, accuracy and precision, simple operation, easy data storage, less prone to noises etc.
इन प्रश्नों का उत्तेर कमेंट में दे |
Check Your Progress 2
1) Distinguish between Microcomputer and Mainframe computer.
2) What are the five basic operations performed by the computer?
3) How can you classify computers according to technology?
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