Computer: Definition
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.
Computer sizes and power
Computers can be generally classified by size and power as follows, though there is considerable overlap:
- Personal computer: A small, single-user computer based on a microprocessor.
- Workstation: A powerful, single-user computer. A workstation is like a personal computer, but it has a more powerful microprocessor and, in general, a higher-quality monitor.
- Minicomputer: A multi-user computer capable of supporting up to hundreds of users simultaneously.
- Mainframe: A powerful multi-user computer capable of supporting many hundreds or thousands of users simultaneously.
- Supercomputer: An extremely fast computer that can perform hundreds of millions of instructions per second.
Personal Computer Types
Actual personal computers can be
generally classified by size and chassis / case. The chassis or case is
the metal frame that serves as the structural support for electronic
components. Every computer system requires at least one chassis to house
the circuit boards and wiring. The chassis also contains slots for
expansion boards. If you want to insert more boards than there are
slots, you will need an expansion chassis, which provides additional
slots. There are two basic flavors of chassis designs–desktop models and
tower models–but there are many variations on these two basic types.
Then come the portable computers that are computers small enough to
carry. Portable computers include notebook and subnotebook computers,
hand-held computers, palmtops, and PDAs.
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 slimline models.
Notebook computer
An extremely lightweight 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 -- small enough
that it can sit on your lap. Nowadays, laptop computers are more
frequently called notebook computers.
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. 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.
