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From: ralf@b.gp.cs.cmu.edu.UUCP
Newsgroups: comp.sys.ibm.pc
Subject: Re: Format problems on AT clone...
Message-ID: <38@b.gp.cs.cmu.edu>
Date: Sat, 13-Jun-87 14:24:39 EDT
Article-I.D.: b.38
Posted: Sat Jun 13 14:24:39 1987
Date-Received: Sun, 14-Jun-87 01:44:12 EDT
References: <717@cod.UUCP> <691@percival.UUCP>
Organization: Carnegie-Mellon University, CS/RI
Lines: 39

In article <691@percival.UUCP> leonard@percival.UUCP (Leonard Erickson) writes:
>I've encountered problems formatting floppies (esp 1.2 meg) on a couple
>of AT clones at work.  Problems occur with both MSDOS 3.1 & PC-DOS 3.1.
>
>I can now format 360k floppies after reducing the number of buffers in
>CONFIG.SYS from 40 to 36. (it works, but _why_?!)
>
>I still couldn't format 1.2 meg disks until I happened to try the 
>"format a disk" option from our user menu program. After much investigation
>I found a "solution". Go into BASIC and type SHELL "FORMAT A:"
...
>Another AT (clone)  will format ok, but after _completing_ the format
>gives a "Track 0 bad, disk unusable" error. The disks *are* usable,
>they pass CHKDSK, Norton''s DT, and Mace Utilities Diagnose. 
>-- 
>Leonard Erickson		...!tektronix!reed!percival!leonard
>CIS: [70465,203]		...!tektronix!reed!percival!!bucket!leonard

Your problems are due to a major omission in *all* versions of FORMAT.  FORMAT,
of necessity, uses several buffers for writing to the disk (FAT's, empty
directory sectors, etc).  Unfortunately, *FORMAT does not check to see whether
its buffers cross a 64K boundary*!!!  Since the DMA chip handles only 16-bit
addresses on its own, an auxiliary register is used to hold the high bits of 
the address.  Thus, an entire read or write operation must take place within
an address block which has the same high bits.  If the buffer you tell the ROM
BIOS to use crosses a 64K boundary, the ROM will return an error.  It is this
error return that prompts FORMAT to give its own error message.

There is only one solution--change the amount of memory used by DOS and any
TSR's until the buffers move off of the 64K boundary.  Changing the number
of buffers will work, as will removing (or *adding*) a resident program.

-- 
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ARPA:  RALF@B.GP.CS.CMU.EDU               USnail: Ralf Brown
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                                                  Carnegie-Mellon University
DISCLAIMER?  Who ever said I claimed anything?    Pittsburgh, PA 15213
"I do not fear computers.  I fear the lack of them..." -- Isaac Asimov