Computer Systems
The term computer is generally applied to a collection of devices that
together are technically known as a computer system. This system
consists of functional components, or parts, for input, storage, control,
processing, and output. All general-purpose computer systems have
these components, but their physical characteristics may vary.
The main storage, control, and processing components constitute
the heart of the computer system. The central processing unit (CPU) has
been designed by the manufacturer to control and carry out basic
instructions to that particular computer. It is here that the data processing
is done. The CPU has two components, called the control and arithmetic
units. These input and output devices are handled by machines called
I/O devices. In later units, more will be said about these machines.
Main storage, which is also called the memory, is made up of
circuits with millions of tiny metal cores that can be magnetized; thus,
they can be in one of two states, magnetized or un-magnetized. Because
it is made up these cores, it is frequently called core storage, or just core.
One often hears of programs not running because they exceeded core.
This means that there are not enough cores to handle all the data that
have been programmed.
The control unit directs the step-by-step operation of the system. It
selects instructions and data from main storage, interprets them, and
controls the flow between main storage and the arithmetic unit. The
latter performs the actual arithmetic operations that are called for in the
instructions. It also performs some kinds of logical operations such as
comparing or selecting information. The control and arithmetic units are
made up of electronic circuits with millions of switches, which can be in
one of two states, either on or off.
Main storage and the CPU are connected to a console, where
manual control operations can be performed. The computer operator can
communicate directly with the machine by means of control keys or a
specially modified typewriter. The operator can stop or start the program
or make corrections in it. The console also includes a display such as
indicator lights or a TV screen so that the operator can monitor
information from the machine.
It is necessary to understand how a program works in conjunction with
the entire computer system. The machine can be programmed to carry out
instructions, or execute them, if they are in machine language, a
communications code that the machine can "understand". The program is a
set of instructions that may also include data to be processed. The computer
is given the program through an input device and places it in main storage
(memory). When the machine is asked to act on the program, the program is
brought into the control unit, which directs the other units to carry out the
steps of the program in sequence. After the data have been processed by the
CPU, the final result is transmitted by means of an output device that makes
the result available to the programmer.