Operating The Computer; Chapter 3 Operating The Computer Under Cp/M; What Is Cp/M - Epson PX-8 User Manual

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Virtual screen
=
Real screen
Function key display area (optional)
The screen allows individual dots of the screen to be lit (bit image mode). This
is only possible by means of software. The most convenient way to understand
this mode is to use BASIC. If this mode is used other than in BASIC, it will
be with special applications software and the appropriate manual should be con-
sulted for its use.
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Chapter 3
OPERATING THE COMPUTER
UNDER CP/M
Chapter 2 discussed the operation of the computer at the simplest level. This
chapter deals with the operation on a day to day level.
It
mainly covers using
the operating system CP
1M,
housekeeping of files and using the utility and ap-
plications programs. For a complete guide to the operation of an applications
program, see the appropriate manual for that program.
3.1 What Is CP/M?
CP
1M
is the most popular operating system for microcomputers. An operat-
ing system is a collection of computer programs which have been assembled
to make it easy for the user to run programs, handle saving and loading of data
and generally allow easy transfer of information between software and hard-
ware. The popularity of CP
1M
is due to the fact that it can be used on a large
number of machines.
To understand what an operating system does, consider the analogy of a tele-
phone system linked to the switchboard of a large company. If anyone dials
into the company the public telephone network handles the connection to the
company. The switchboard in the company then directs the caller to the person
to which he wishes to speak. Similarly, if a person inside the company wishes
to callout, he again goes through the switchboard to reach the public telephone
system.
CP/M
is very much like this except that there are a number of 'switchboards'
for different parts of the hardware, e.g. the disk, Microcassette and devices
such as the keyboard and screen. An"yone writing software for a CP
1M
based
machine only has to use the equivalent of the public telephone system in this
analogy. This means that having written a program such as a word-processor,
it requires little if any further programming to allow the program to be run
on a computer other than the one for which it was originally designed, provid-
ing both computers use the CP
1M
operating system. All interfaces between the
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