Computers are electronic devices that can follow instructions to accept input, process that
input, and produce information. There are four types of computers: microcomputers, minicomputers,
mainframe computers, and supercomputers.
Microcomputers, also known as personal computers, are small computers that can fit on a desktop.
Portable microcomputers can fit in a briefcase or even in the palm of your hand. Microcomputers are
used in homes, schools, and industry. Today nearly every field uses microcomputers.
One type of microcomputer that is rapidly growing in popularity is the portable computer,
which can be easily carried around. There are four categories of portable computers.
Laptops: laptops, which weigh between 10 and 16 pounds, may be AC-powered, battery-powered,
or both. The AC-powered laptop weighs 12 to 16 pounds. The battery-powered laptop weighs 10 to 15
pounds, batteries included, and can be carried on a shoulder strap.
Notebook PCs: notebook personal computers weigh between 5 and 10 pounds and can fit
into most briefcases. It is especially valuable in locations where electrical connections are not
available. Notebook computers are the most popular portable computers today.
Subnotebooks: subnotebooks are for frequent flyers and life-on-the-road types.[1] Subnotebooks
users give up a full-size display screen and keyboard in exchange for less weight. Weighting between
2 and 6 pounds, these computer fit easily into a briefcase.
Personal Digital Assistants: much smaller than even the subnotebooks. Personal Digital
Assistants (PDAs) weigh from 1 to 4 pounds. The typical PDA combines pen input, writing
recognition, personal organizational tools, and communication capabilities in a very small
package.
Minicomputers, also knows as midrange computers, are desk-sized machines. [2]They fall into
between microcomputers and mainframes in their processing speeds and data-storing capacities.
Medium-size companies or departments of large companies typically use them for specific purposes.
For example, they might use them to do research or to monitor a particular manufacturing process.
Smaller-size companies typically use microcomputers for their general data processing needs, such as
accounting.
Mainframe computers are larger computers occupying specially wired, air-conditioned rooms
and capable of great processing speeds and data storage. They are used by large organizations
business, banks, universities, government agencies—to handle millions of transactions. For
example, insurance companies use mainframes to process information about millions of policyholders.
Supercomputers are special, high-capacity computers used by very large organizations principally
for research purposes. Among their uses are oil exploration and worldwide weather forecasting.
In general, a computer's type is determined by the following seven factors:

The type of CPU. Microcomputers use microprocessors. The larger computers tend to use
CPUs made up of separate, high-speed, sophisticated components.
The amount of main memory the CPU can use. A computer equipped with a large
amount of main memory can support more sophisticated programs and can even hold several
different programs in memory at the same time.
The capacity of the storage devices. The larger computers systems tend to be equipped
with higher capacity storage devices.
The speed of the output devices. [3]The speed of microcomputer output devices tends to be
rated in terms of the number of characters per second (cps) that can be printed usually in tens
and hundreds of cps. Larger computers' output devices are faster and are usually rated at speeds
of hundreds or thousands of lines that can be printed per minute.
The processing speed in millions of instructions per second (mips). The term instruction
is used here to describe a basic task the software asks the computer to perform while also
identifying the data to be affected. The processing speed of the smaller computers ranges from 7
to 40 mips. The speed of large computers can be 30 to 150 mips or more, and supercomputers
can process more than 200 mips. In other words, a mainframe computer can process your data a
great deal faster than a microcomputer can.
The number of users that can access the computer at one time. Most small computers
can support only a single user, some can support as many as two or three at a time. Large
computers can support hundreds of users simultaneously.
The cost of the computer system. Business systems can cost as little as $500 (for a
microcomputer) or as much as $10 million (for a mainframe) and much more for supercomputer.