Page 147 - Standard Handbook Of Petroleum & Natural Gas Engineering

132 Mathematics

System Hardware

System hardware consists of the central processor, the input devices (usually
a keyboard), the output devices (probably both a video display terminal and a
hardcopy printer), long-term storage devices, and perhaps communications
components. In smaller systems, more than one of these components may be
“built in” to one unit, while in larger systems there may be many units each of
several components associated with the system.
The central processing unit (CPLJ) consists of the arithmetic-logic unit (ALU),
the control unit, and the central storage (short-term memory) unit. The CPU is
normally classified by size of the word (number of bits in one piece of infor-
mation or address), size of memory (which is partly dependent upon the size
of the word available and is expressed in KB, i.e., kilobytes) and by speed of
operations (given in megaHertz, mH). There are many combinations of these
factors, depending upon the processor chip used and upon the architecture of
the machine. Speed of operation and of data transfer is of major importance
in large number-crunching programs. Memory size affects the size of the
program and the amount of data that may be held at one time, while word size
primarily affects the size of memory available. A useful addition to the system,
if a need for large-scale number crunching is anticipated, is the arithmetic co-
processor chip, which performs high-speed numerical operations.
Keyboards are the most widely used input devices, but optical scanners and
digital pads (for computer-aided design) are some additional input devices. Input
may also be from files stored on a disk or tape.
Video display terminals for output are available in several sizes (measured
diagonally in inches), various resolutions (number of pixels, an important factor
in graphics) and a choice of monochrome or color. The type of screen chosen
will depend upon the anticipated use. Hardcopy output devices usually include a
printer, either a dot-matrix printer, in which the characters are formed by dot
combinations, or a laser printer. The number of dots per character unit is one
consideration in the quality of print in a dot-matrix printer, although options
such as double-strike may increase the print quality at the cost of speed. Speeds
of laser printers (as opposed to the larger line printers) are measured in pages
per minute (ppm), but the actual throughput on printers is not always a direct
correlation of ppm. Laser printers have become available at affordable prices
and have the major advantage of producing a much lower level of noise, as well
as of high-speed operation. For engineering and design use, plotters, either
black-white or multicolored are frequently added to the system. Output may also
be sent to a disk or tape for long-term storage.
Long-term memory storage devices may be cassettes, for small amounts of storage
on personal computers, several sizes of floppy diskettes, hard (fixed) disks or
magnetic tapes (frequently used for duplicate “back-up” storage). This choice
can be based on the amount of available storage needed without changing
cassettes or floppy diskettes and on the speed of access to the device required,
with cassettes being the slowest and hard disks the fastest accessed devices.
Systems may also include modems, which connect small computers or terminals
to other computers or workstations either in-house or over telephone system lines
and whose speed of transmission is rated by baud (for binary information units,
the number of bits transmitted per second). Common baud rates for small
systems are 2400 or 9600 with higher rates possible. Computers may also be
networked together to share data or peripheral components such as high-
speed printers.