Date   : Thu, 02 Nov 1989 09:36:39 EST
From   : SAGE@LL.LL.MIT.EDU
Subject: on the other side of the floppy ...

>> A friend of mine wants to know how to do a CP/M bios (BDOS) call to
>> read/write side 1 of the floppy disk (vs side 0). He knows where the
>> disk controller is and he can do whatever he wants to either sides
>> of the floppy by writing to it directly and bypassing BDOS. What he
>> wants to know is how to do it via a BDOS call; or how to set it up
>> such that the BDOS call will read side 1 of the disk.

   Dealing with hardware details does not fall within the province of
the BDOS.  A clue to this is the fact that *ALL* CP/M-2.2 computers use
the very same BDOS code, despite many hardware differences (some use
hard disks, RAM disks, or floppies; the floppies are single-sided or
double-sided, 48-tpi or 96-tpi, 8" or 5", etc.).  The BDOS deals with
disks at the file level, not at the physical sector and side level.

>> I have a CP/M Plus card for my Apple //e made by ALS (who no longer
>> exists) and it came with plenty of documentation, all by Digital
>> Research.  However, they were no help what-so-ever when it comes to
>> accessing side 1 of the floppy.  May be because my computer does not
>> understand side 1 since it doesn't have double sided disk drives!!

   You should not expect Digital Research to help with this, as it has
nothing to do with CP/M.  All the hardware-specific information is in
the BIOS, which is supplied by the computer designer and not by DRI.

   Even the BIOS, by the way, does not deal with the hardware at the
'side' level.  Externally, it is required to select a specified track
and sector number only.  It is a BIOS internal function to decide on which
side a sector of a given number is located.  So, I think your friend
cannot use the operating system to select a specified side of the
diskette; he will have to, as he is now, use code that directly accesses
the disk controller.



End of INFO-CPM Digest V89 Issue #198
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