SB BBC @ GBR
Oldie hints/tips #084-086
Hints and tips from the archives of Wakefield BBC Micro User Group...

84. *SAVE bug
    ~~~~~~~~~
It is useful to be able to save very long dummy files when reserving disc
space for random access files, (or for other purposes), as recommended in the
Acorn DFS User Guide. The syntax is *SAVE 0 N or *SAVE 0+N, where N is the
length in Hex. This is very fast, and works fine on the 1.20 Acorn DFS,
(DNFS). However, on the 0.90 Acorn DFS, horrible things happen as soon as N
exceeds &FF00, (just under 64k), and the disc tends to be corrupted. The
alternative is use OPENOUT, and advance PTR# to the required length. In the
example below, an 88k file can be reserved, albeit very slowly. The DNFS is
much faster than the 0.90 all round, but the difference is particularly
noticeable when you are using Random Access Filing, and it's worth upgrading
if you can get hold of the EPROM.

The Acorn 1770/1772 DFS does not suffer from this problem.

Remember that 1k is 1024 bytes, so PRINT &16000/1024 gives the answer 88k.

10 chan=OPENOUT("name"):PTR#chan=&16000:CLOSE#chan

85. Disc drive hints
    ~~~~~~~~~~~~~~~~
*BACKUP produces a duplicate of the original disc, with all the files,
(programs), in the same order on the disc. *COPY, on the other hand, reverses
the order on the disc. The catalogue will not show this up, as it is always
in alphabetical order, but you can tell if you use *COMPACT or *INFO.

If you use a '*' command which none of the ROMs recognize, then the Acorn
DFS's will attempt to *RUN a file of that name. If the file is not a
machine-code routine, then the attempt will fail. However, the Watford
DFS's go one step further, because they will *EXEC the file if it is text,
(ie if it has been SPOOLed onto disc).

This was written before the Master and the 1770 DFS came out. I think 
that they too are semi-intelligent in this situation.

86. Formatted disc speed
    ~~~~~~~~~~~~~~~~~~~~
You can get faster response times from your disc just by using the right
formatting program. Each floppy has a small index hole near the large centre
hole. Some formatters put sector 0 after the index hole on every track. The
effect of this is that each time the head steps from one track to the next,
it misses the start of sector 0, causing a delay until the index hole comes
round again. The better formatters provide an offset of several sectors
between each track to allow the head to settle after stepping. The following
program was used to compare different formatters.

10 *CAT        Return Head to Track 0 and spin disc.
20 TIME=0
30 *VERIFY     Must have Watford DFS or Disc Doctor.
40 PRINT TIME

The Watford DFS formatter is one of the slowest, somewhat surprisingly being
beaten by a BASIC program available free on Micronet. Disc Doctor has a very
fast formatter, and the Cumana program is also good.

Further improvements in speed can be achieved by moving frequently accessed
small files to the outer edge of the disc, i.e. nearer to the catalogue.
The prime candidates for this treatment are the !BOOT and MENU files. These
files are usually added as an afterthought when the disc is complete, thus
placing them near the centre of the disc. This results in much tracking
noise, wasted time and head wear each time the disc is booted. Far better
to put dummy !BOOT and MENU files on the disc immediately after formatting
it, ensuring that these vital files reside (mostly) on track 0.

(One way to save a dummy file is to use *SAVE !BOOT 0 1, but this only
reserves one sector of 256 bytes, but you can use *SAVE MENU 0 n00, where n
is the number of sectors to be reserved.)

NB: This was written before the Acorn 1770 DFS was released; this does of
    course support the *VERIFY command.

73 Rick G4BLT @ GB7WRG