hamilton@uxc.cso.uiuc.edu (08/27/87)
/* Written 9:12 am Aug 20, 1987 by samperi@magpie.UUCP in uxc.cso.uiuc.edu:comp.sys.ibm.pc */
/* ---------- "Absolute floppy disk sector read/wr" ---------- */
It seems that the DOS interrupt 0x25 (absolute disk sector read) can only
be used to read the first 720 sectors on a high density floppy (installed
in the high density drive of an AT). I've had to use the bios disk service
2 in order to read all 2400 sectors. Is this a DOS bug?
/* End of text from uxc.cso.uiuc.edu:comp.sys.ibm.pc */
no, it's probably a feature. a while back, i wanted to read some
non-dos 1.2Mb disks using the absolute disk sector routines. i also
had a problem at 720 sectors. however, i noticed that if i forced
dos to believe there was a 1.2Mb diskette in the drive (by DIRing a
dos disk there, then changing diskettes), it worked fine. i suspect
that until dos sees a media type byte for 1.2Mb, it assumes any diskette
in that drive is only 360Kb.
what i probably should have done is use the BIOS level functions.
i think there is a subfunction that allows you to tell the BIOS that
you have a 1.2Mb diskette.
wayne hamilton
U of Il and US Army Corps of Engineers CERL
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