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Configuration for the H89-17
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An operating system is more than just a collection of programs that perform
various functions, such as communicating with peripherals or finding data on a
diskette. The central idea is that the software system is logically organized. All
its programs are available to you at any
ti~e,
for specific purposes, by means of
operating system "commands".
A portion of the operating system called the "Monitor" is in command of the
other portions. It controls the decoding of commands and temporarily passes
control to subprograms, which carry out the commands. After each operation is
completed, control returns to the monitor, which awaits the next command.
Thus, the monitor is like a switchboard operator who handles communications
for a busy city.
Files
The operating system establishes this communication between hardware and
software by means of a data structure known as a "file". If you consider a disk
drive as if it were a filing cabinet, then the sectors on the diskette correspond to
sheets of paper within the filing cabinet. The disk file is then analogous to a
folder within the cabinet, with a label on it, which contains a number of the
sheets of paper. In other words, a file is an organized group of disk sectors.
Whether you keep the files in an office filing cabinet or on a diskette, you must
organize them in a way that allows you to find them easily. A new file must be
inserted into its proper place, and old files that are changed must be replaced for
future reference.
In this sense, an operating system is like a clerk who keeps track of a great deal of
information, or a librarian who must know where all the books are found. The
operating system must: find space on the disk for new files; give each file a name
that allows it to be cross-referenced; be able to copy data from one file to another;
and be able to re-name, update, and delete files. Above all, the operating system
must be able to communicate with you and carry out your commands quickly
and efficiently.
Under HDOS, each file consists of one or more "clusters", where each cluster is
composed of two contiguous sectors. HDOS automatically increases the size of
files, as required, in increments of one cluster. Therefore, the size of an HDOS file
can run from 512 bytes, which is two 256-byte sectors, up to the total available
space on a diskette.
In order to communicate with the operating system, you or your program must
issue commands. The exact command syntax is discussed in the HDOS Manual.
In some cases, the commands will be issued from the system console.
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