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dostip.003
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2006-10-19
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Use of DSKO$ with POWR-DOS
--------------------------
The DSKO$ function of POWR-DOS has the general syntax:
DSKO$ SW, SE, AD
where
o SW is a Switch (SW=0 for read from disk to RAM; SW
non-zero for write from RAM to disk)
o SE is the disk sector number operated on (0 to 79)
o AD is the start (low end) of the RAM block used as a
buffer; must be 1292 bytes long and cleared before use
-- e.g., CLEAR 0, MAXRAM-1292.
This command allows POWR-DOS to pull in a sector from disk, modify
individual bytes, or groups of bytes (up to a sector in length),
and write the modified sector back to the disk.
This function requires that the disk be formatted, but not that
there be a directory.
This would seem to allow some pseudo-formatting, to get
sub-sectors ("blocks") on the disk. For example, each 1292 byte
sector could be considered as a set of four 323 byte blocks (320
total blocks on a disk); since 1292 factors into 4*17*19, there
are other possibilities. Each block could be used as a data
"record" (without a directory structure, a dedicated data base is
about the only application I can think of for a disk used this
way). Each block could hold it's block number (may not be needed)
and data in a format determined by a (to be developed) data base
program.
With SE as the sector number, the block number would be given by
4*SE+OF, OF is an offset within each sector (OF is 0 to 4, in the
above example). Bytes within a block would be identified by an
index BT (0 to 322 in this case).
Although this has some interest, I'm not likely to pursue it
further myself -- since data bases on the Model 100 are not an
interest of mine (my data bases are all too big to fit even on a
Chipmunk disk!).
A down side of this is that the total sector must be read and
written to replace any one of the blocks -- suggesting a
four-times speed-up if the disk were truly formatted into smaller
sectors. From the published data, TS-RANDOM (Traveling Software)
appears to do just that.
BUT -- although I have not tried it, the POWR-DOS manual says that
disks formatted with FORMAT.BA (part of the POWR-DOS package) will
accept sector (DSKO$) writes almost 20 times faster than normally
formatted disks -- so long as they have not been written to by any
file based command.
Phil Wheeler [71266,125]
Torrance, CA
10/11/86