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From: wayne@schaefer.MATH.WISC.EDU (Rick Wayne)
Newsgroups: comp.sys.ibm.pc
Subject: Magic Number Five in turbo C, MS C, and int 21/0E
Keywords: drives, C programming
Message-ID: <483@schaefer.MATH.WISC.EDU>
Date: 10 Oct 89 16:03:15 GMT
Organization: Mathematics Department, University of Wisconsin - Madison
Lines: 29

we've run into a little problem here that i find baffling.  we're trying to
determine the number of disk drives on a machine at runtime.  there's a DOS
interrupt service for this: interrupt 0x21, function 0x0E, "set default
disk drive".  it's supposed to return the number of drives in the system.

for all the machines we have here (AST Premium 386, Standard 286, Compaq
Deskpro, Dell 210), we get the answer of...five.  needless to say, these
disparate machines have differing numbers of drives.  the one number we
CANNOT come up with, of course, is five.

well, ok, i can't read, maybe a misprint, i'm reading the register wrong, who
knows.  i'll try using the setdisk() function in turbo C, which is supposed
to return the right value.

Five.

Microsoft C?  Five.  hmm.  a sort of subtle pattern emerges.

have we discovered a secret numerological cabal here?  (i have been approached
in parking lots by religious nuts convinced that the number 666 was being 
seeded millions of times in the nation's computers to assist a Satanic 
takeover).  i am a little frustrated, to say the least.  many of our machines
are using a special disk device driver to allow partitions >32 MB, but not
all of them.

any ideas, troops?

rick wayne
WISPLAN (UW Extension)