I-
80
columns
8th
lines
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.
2-58
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
3-1
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