FREE online courses on the Basics of a Computer - CLASSIFICATION OF COMPUTER
SYSTEMS -According to size and memory capacity
This classification, nevertheless,
is still very very unconditional. If a survey were to be conducted among the top
computer personnel and the difference between a micro and a mini asked, a dozen
different answers would result. Computer technology changes so fast that a mini
today could be known as a micro after one year's time. In fact the distinction
between the different types of classified computers is decreasing day to day.
A personal Computer (PC) or a
micro is the smallest general purpose computer system which can execute programs
to perform a variety of instruction. It has all the functional elements found in
a larger system. These computers usually have an 8, 16 or a 32 bit
microprocessor.
The cheapest variety is one with
an 8 bit microprocessor. All 8 bit micros are built around a few popular
microprocessors like the Z80, 8080 etc. By an 8 bit microprocessor it is
understood that it can process 8 bits or 1 byte of data at a single given time.
These microprocessors have a 16 line address bus and hence they can identify a
maximum of 2 16 i.e. 65,536 or 64K address locations.
In the 16 bit micros the data is
processed 16 bits at a time. An example of a 16 bit microprocessor is the Intel
8088 used by the IBM PcJr and the Intel 8086. These microprocessors usually have
an expanded 20 line address bus. Hence they identify a maximum of 2 20 i.e.
1,048,576 or 1 M address locations. This eliminates one of the limitations of 8
bit computers i.e. of main RAM memory. Whereas the 8 bit computers can only have
a maximum of 64 K RAM the 16 bit computers can have up to 1 M of RAM memory.
Usually, however, the 16 bit computers come with 256 K RAM with the facility to
expand. If necessary, extra bus lines can be adapted to increase the main memory
capacity.
The latest introduction is the
Motorola 68000 which is a 32 bit chip. This can process 32 bits of data at a
given time. It has an expanded 24 line address bus which gives it a tremendous
potential of accessing up to 2, 24 or 16 M address locations, thereby increasing
the potential main RAM memory to 16 M.
The peripherals possible with the
micros are varied. Virtually all micros come with a QWERTY type keyboard as an
input device. A light pen, mouse etc, can also be used as input devices. The VDU
is the most common output display unit. It can be connected with a variety of
printers, plotters and also speakers. These micros can easily be connected with
a modem and hooked up to mainframe system, thereby acting as intelligent
terminals. Storage can be done on floppy disks, Magnetic tapes, Winchester etc.
The peripherals devices of computer systems will be dealt with later on in this
book. Some of the most popular commercially available micros are the IBM PcJr,
Apple Commodore, Hewlett Packard, BBC Micro etc.
Through it is almost impossible to
define a minicomputer system anymore; an arbitrary definition can be resorted
to. This is the way it goes: "A minicomputer system is a small general purpose
computer varying in size from a desktop model to a unit the size of a four
drawer filing cabinet". It is quite obvious that there is tremendous amount of
similarity between the more powerful micros and the lower end minis. The same
situation exists on the other end where the lower priced mainframes are almost
similar to the higher priced minis. In fact the minicomputer manufacturers are
almost being wiped out with the advent of the super micros. Today's typical mini
will surpass the PC in storage capacity, speed of arithmetic operations and
ability to support a variety of peripherals. Minis are usually multi-user
computers in contract to the micros. They were previously available with the 16
bit microprocessor but nowadays are available only with the 32 bit one. One of
the most important uses of minis is in Distributed data processing networks.
A whole series of mainframe
models, ranging in size from small to very large, are typically lumped together
under a family designation by mainframe manufacturers. The primary and on-line
storage capabilities increase. Several microprocessors are used in place of the
single microprocessor used in micro and minicomputer systems. The result is that
these systems can process data much faster. These systems have the flexibility
to operate automatically from 2 to 8 bytes in the same unit of time. The
mainframe vendors also have much large libraries of application programs. One of
the most versatile and popular mainframes available is the IBM 370.
Supercomputers are the most
powerful and expensive computers made. Only a few of these computer mostres are
made each year because only a few people need it. These computers are a national
resources These computers are designed to perform scientific application and
hence the computational speed is very important. To maximize the speed each
address location holds 64 bits of information. The time required to execute a
single operation may be as slow as 4 nanoseconds. The prices of these computers
range from 4 million to 215 million dollars. Cray research and control Data
Corporation are the primary builders of super computers in
U.S.A.
Not all super computers are designed for scientific work. Some computers have
been used for producing computer generated images in films.
