GENERATIONS OF COMPUTERS
Now-a-days, it has been extended to include both the hardware and software which together make up an
entire computer system. Although there is a certain amount of
overlapping among the generations, the approximate dates shown against each
other are normally accepted.
FIRST GENERATION (1945-59)
Vacuum tubes were used as main electronic component in first
generation computers. These computers were very large in size and having
limited memory. These were consumed large amount of electricity and produced
large amount of heat. These were unreliable computers. The first generation
computers were IBM- 650, UNTVAC- 1, ENIAC, etc.
SECOND GENERATION (1959-1965)
In second generation, transistors were used. These computers were
made from semiconductors mainly silicon and germanium. In these computers,
magnetic core was used as the internal storage. The high level language was
used to instruct the computers to perform the tasks. The second generation
computers were control Date 3600, 7000 series, IBM 1400 series, etc. These
computers required less power to operate. These were more reliable and faster
than first generation.
THIRD GENERATION (1965-1974)
In third generation, integrated circuits (ICs) on chips were used
to store data and process instructions. These computers could handle more than
one operation simultaneously. Third generation computers were ICL-1900 series,
IBM-360 series, etc. In this generation, monitor and keyboards were used for
input and output. More advanced high level languages including PASCAL, COBOL
were used for programming. In this generation, magnetic disk used for external
storage.
FOURTH GENERATION (1974-1980)
Large scale integration (LSI) and very large scale integration (VLSI) chips which packed about 50,000
transistors in a single chip are used as the primary storage
medium and provided fast processing speed with more reliability. The fourth
generation’s computers are HP 3000, IBM-370, Burroughs 87700, etc. In this,
disk memory became very large. In this, semi-conductor
primary storage is used. In this generation, magnetic disks became the primary
means of external storage and further miniaturization in which complete circuits
are reduced to virtually microscopic size, hundreds of circuits may be placed
on a chip of the size of a pinhead. In this, microprocessor were used.
FIFTH GENERATION (PRESENT)
This generation have mainly emphasis in the field of parallel
processing and artificial intelligence (AI). The main aim of this generation is
to make computer intelligent like human being. Super computer and Robot are the
results of this generation.
CLASSIFICATION OF COMPUTERS
Computers in general can be divided into two main parts.
CLASSIFICATION
ACCORDING TO THE LOGIC USED ACCORDING TO LOGIC USED, COMPUTERS ARE FURTHER
DIVIDED INTO THREE PARTS.
(a) Analog Computers
To measure the physical quantities like pressure, speed, etc.
analog computers are used. These take input data in the form of signals and
convert them to numeric values. These computers are mainly used for scientific
and engineering purposes, because they deal with quantities that vary
constantly. They give only approximate results, e.g. A thermometer does not
perform any calculations but measures the temperature of the body.
(b) Digital Computers
Digital computers deal with counting. These are high speed
programmable electronic devices that perform mathematical calculations, compare
values and store the results. They recognize data by counting discrete signals
representing either a high/low or on/off voltage state of electricity. They
take input data and instructions in the form of digits 0 to 9, alphabets A to Z
or special characters, and produce the output in the same.
(c) Hybrid Computers
There are lots of applications, in which one wants to observe the
variations in the signals and according to these variations he wants to take an
action. Most of these variations are such that it may not be possible to check
it manually. On the other hand, the action to be taken is so fast that it is
impossible for human beings to perform the action in the required time. Hybrid
computers are computers which handle such applications. These computers have
the features of both digital and analog computers.
2. CLASSIFICATION
ACCORDING TO THE SIZE OF COMPUTERS
According to the size, computers are further divided into various
parts.
(a) Micro Computers
In micro computers, microprocessor performs the function of ALU
and control unit. The microprocessor linked with primary memory, input, output
and secondary storage devices. These computers are single user operating
systems, e.g. Home computer, PCs, etc. Home computers consist of a single unit,
look like a small keyboard, but it has a CPU, memory unit and other circuitry.
We can attach TV and Audio tape with them as input/output device. PCs are
single user systems. PCs have a separate monitor for display and floppies or
Winchester drives for backing storage. E.g. PC, PC/XT, PC/AT, etc.
(b) Mini Computers
These computers are more expensive. They use microprocessor as CPU
and can handle the needs of multi-user environment. They use 16 bits or 32 bit
microprocessors. Motorola 68020 and intel 80386, 80486, 80586 are examples of
microprocessors of these computers. They have atleast 1 MB RAM. They can
support multiple I/O devices. These are mainly used in Banks and Railway
Stations. These computers mainly used Unix operating system. E.g., PDP-11,
Magnum, etc.
Mainframe Computers
These computers are more powerful and large in size. They have
high storage capacity and can process large amount of data very fast. They have word length of. 32 bit, 48 bit
or 64 bit. They have. U memory size ranged
from 1 MB to 16 MB. They can support more than 100 users in time-sharing mode.
Super Computers
Super computers are mainly used in scientific and statistical
applications like weather forecasting, air flow, etc. where large amount of
data is to be manipulated in very short period. They are capable of executing
multi million instructions per second. They are multi-processor system and each
processor does parallel processing. These are powerful and very expensive.
E.g. NEC-500, IBM 3090, CRAY XMP-24, etc.
Palmtop Computers
Palmtop computers accept handwritten inputs, using an electronic
pen which can be used to write on a Palm’s screen, having small disk storage
and can be connected to a wireless network. One has to train the system on the
user’s handwriting before it can be used. A Palmtop computer has also the
facility to be used as a mobile phone, Fax and e-mail machine. A version of
Microsoft operating system called Windows- CE is available for palmtop
computers.
Laptop Computers
Laptop PCs are portable computers weighing around 2 kgs. They have
a keyboard, flat screen known as LCD (liquid crystal display) and a Pentium or
power PC processor. Colour displays are available. They normally run using
Windows OS. Laptops come with hard disk, CD ROM and floppy disk. They should
run with batteries and are thus designed to conserve energy by using power
efficient chips. Many laptops can be connected to a network. There is a trend
towards providing wireless connectivity to laptops so that they can read files
from large stationary computers. The most common use of laptop computers is per
word processing and Spreadsheet computing.
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