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CHAPTER ZERO
Other commands may be included. in a program written in BASIC or assembly
language. These will allow a process to "open" and "close" files, and to perform
read/write operations on the files. Refer to the appropriate language manual for
the proper command syntax.
Controlling the Peripherals
An operating system must also manage all the peripherals in the system. This
allows you to type-in commands from the system console, and have the operat-
ing system perform some I/0 function without your intervention. You may also
include such commands in your programs without having to write detailed
instructions for controlling the peripherals. The operating system will take care
of the ''messy details''.
HDOS uses programs called "device drivers" to control peripherals. Each device
driver is written with the characteristics of a particuliar peripheral in mind. Its
speed, line length, and "handshaking" capability are examples of the charac-
teristics. For standard ASCII serial peripherals, the device drivers may differ
only in minor details. They may be unique for other devices such as paper tape
punches or X-Y plotters.
However, all device drivers have one thing in common. After they are written,
one for each peripheral, they become a part of the operating system. It is not
necessary to include the drivers in each program which uses the peripherals
because these programs can simply issue I/O requests to the operating system.
This can save a great deal of space in each program because the instructions for
controlling the peripherals need not be repeated.You can also make a program
communicate with many different peripherals, without rewriting it, by simply
redefining the appropriate device drivers.
Programs running under HDOS are called "device independent". Each
peripheral is given a symbolic name, much like a file. For instance, the system
console is referred to as "TT:", and
"SY~:"
identifies the system disk drive. The
colon (:) at the end of each name identifies it as that of a device name rather than a
file name.
Transferring Data
Data can be copied from file to file. It can also be copied from a file to a device, or
from a device to a file. To create a new file with data typed-in from the console,
you simply command HDOS to copy from your terminal to a unique file name.
Refer to the HDOS Manual for the syntax of such commands.
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