Path: utzoo!attcan!uunet!snorkelwacker!apple!altos!altos86!rcollins
From: rcollins@altos86.Altos.COM (Robert Collins)
Newsgroups: comp.sys.ibm.pc.misc
Subject: Re: AT CMOS Fixed Disk Type
Keywords: AT CMOS Disk
Message-ID: <4084@altos86.Altos.COM>
Date: 18 Sep 90 21:46:39 GMT
References: <1990Sep18.100108.9119@ux1.cso.uiuc.edu>
Reply-To: rcollins@altos86.UUCP (Robert Collins)
Distribution: comp
Organization: Altos Computer Systems, San Jose, CA
Lines: 53

In article <1990Sep18.100108.9119@ux1.cso.uiuc.edu> dslg0849@uxa.cso.uiuc.edu (Daniel S. Lewart) writes:
>I just managed to zap the CMOS on my IBM PC AT.  In order to recover, I ran
>SETUP from the Diagnostic disk.  At one point, it asks me for the Fixed Disk
>Type which is supposed to be in the range 1-47.  Here are my questions:
>
>1) How can I figure out what the appropriate number is?

* Open the computer up and get the drive manufacturer and model number.
* Use that number to obtain how many cylinders, heads, and write precomp
  the drive uses.  (no write precomp is -1, or FFFF) 
* Convert these numbers to hex.
* Go into debug and look at F000:E401 (this is the hard disk parameter
  table.  The format of the table is as follows:
  DW	# OF CYLINDERS
  DB    # OF HEADS
  DW	0
  DW	WRITE PRECOMP
  DB	0
  DB	CONTROL BYTE 
  DB	3 dup (0)
  DW	LANDING ZONE
  DB	# SECTORS/CYLINDER
  DB	RESERVED FOR FUTURE USE
  As you can figure from this description, each entry is 16 bytes.
  Therefore, the entry at F000:E401 maps to drive type 1.  The
  entry at F000:E411 maps to drive type two.  Etc.
* Find the drive type that matches your manufacturers parameters.
  (just match the cylinders & heads on your IBM AT)
* DRIVE TYPE = ((DRIVE_TABLE_ADDR - E401) / 10H)

That should take care of you.

>2) What does it mean?

It is an index into the table I just described.

>3) Is there a table of type values somewhere?

Yes, it is at F000:E401.  After you set the drive type, and boot your
computer, look at the INT41 vector.  INT41 is a pointer to the drive
parameter table entry for device 80h, and INT46 is a pointer for
device 81h.  If you take the DWORD address at 0:4*41h (0:104h) you
will notice it points to your DRIVE_TABLE_ADDR!

Hope this helps



-- 
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