The basic components of a microcomputer
system are:
A central processing unit (CPU).
A memory, comprising both ‘read/write’ and
‘read-only’ devices (commonly called RAM and ROM respectively).
A mass storage device for programs andjor
data (e.g. a floppy and/or hard disk drive).
A means of providing user input and output
(via a keyboard and display interface).
Interface circuits for external input and
output (I/O). These circuits (commonly called ‘ports’) simplify the connection
of peripheral devices such as printers, modems, mice, and joysticks.
In a microcomputer (as distinct from a mini
or mainframe machine) the functions of the CPU are provided by a single VLSI
microprocessor chip (e.g. an Intel 8086, 8088, 80286, 80386, 80486, or
Pentium). The microprocessor is crucial to the overall performance of the
system.
Indeed, successive generations of PC are
normally categorized by reference to the type of chip used. The ‘original’ PC
used an 8088, AT systems are based on an 80286, ’386 machines use an 80386,
and\ so on.
Semiconductor devices are also used for the
fast redd/write and readonly memory. Strictly speaking, both types of memory
permit ‘random access’ since any item of data can be retrieved with equal ease
regardless of its actual location within the memory.
Despite this, the term ‘RAM’ has become
synonymous with semiconductor read/write memory. (VLSI means very large scale
integration, i.e. a complex chip.) The semiconductor ROM provides non-volatile
storage for part of the operating system code (this ‘BIOS’ code remains intact
when the power supply is disconnected).
The semiconductor RAM provides storage for
the remainder of the operating system code (the ‘DOS’), applications programs
and transient data (including that which corresponds to the screen display).
It is important to note that any program or
data stored in RAM will be lost when the power supply is\ switched off or
disconnected. The only exception to this is a small amount of ‘CMOS memory’
kept alive by means of a battery.
This ‘battery-backed’ memory is used to
retain important configuration data, such as the type of hard and floppy disk
fitted to the system and the amount of RAM present.
TIP
It
is well worth noting down the contents of the CMOS memory to avoid the
frustration of having to puzzle out the settings for your own particular system
when the backup battery eventually fails and has to be replaced. To view the
current CMOS configuration settings press the ‘Del’ key during the bootup
sequence and enter the ‘Setup‘ routine.
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