The *MAP command produces a rather cryptic list of the areas of the disc which
are free. If you issue a *MAP command you might get a table like this:
Address : Length
000002 : 00000A
00014A : 000043
0001E3 : 00013D
The list you see may be shorter or longer than this, and the numbers it displays
will certainly be different. Each entry consists of a disc address and the amount
of space free at that location. Both numbers are given in hexadecimal.
The ADFS keeps this free space list automatically, and updates it whenever
files and directories are created and deleted. Because free space is broken up
across the disc it is quite possible for sufficient space to be available to save a
file but for it not to be contiguous on the disc (which is a prerequisite of the file
structure). It may therefore be neccessary, on occasion, to compact the disc
and the computer may warn of this with the 'Compaction required' error.
Compaction shuffles the files around on the disc to close up the free space 'holes'
and leave the largest possible area of contiguous free space.
Just like the *COPY command, *COMPACT makes use of as much shadow
screen memory as possible. When you issue the command:
*COMPACT
the red drive light will glow, and may continue to do so for up to a couple of
minutes. When it goes out, you will find that a *MAP command reveals a few
large chunks of free space on the disc. You can then return to your previous
screen mode and continue with your work.
MOS Filing System commands
What follows is a discussion of some general-purpose commands that the MOS
operating system provides for use with any filing system; in the examples that
follow, use of the ADFS is assumed. These commands provide advanced
facilities which are likely to be employed mainly by experienced computer
users; you should not feel under any obligation to read this information on your
first pass through the Guide.
A note about the ROM Filing System
The reader should be warned that, because of the read-only nature of the ROM
Filing System (RFS), a proportion of what follows is not relevant to its use.
Specifically, the RFS does not implement any commands which attempt to
create or alter files, and thus does not support *SAVE, *SPOOL, *BUILD,
*CREATE or *APPEND.
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