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From: ronald@ibmpcug.co.uk (Ronald Khoo)
Newsgroups: comp.unix.xenix
Subject: Re: XENIX 2.2.3 and >1024 h.d. cylinders: possible?
Summary: No 1024 limit, Don't translate if you can avoid it.
Keywords: xenix, hard disk, cylinders, ESDI
Message-ID: <57c7.250ef512@ibmpcug.co.uk>
Date: 14 Sep 89 00:47:14 GMT
References: <13569@well.UUCP> <5364@tank.uchicago.edu>
Organization: The IBM PC User Group, UK.
Lines: 39

In article <5364@tank.uchicago.edu> goer@sophist.UUCP (Richard Goerwitz) writes:
>
>Re big Wren drives > 1024 cylinders
>
>You can always use the option, available via your WD1007 controller,
>of formatting the drive as usual, but having the controller make it
>appear to the operating system as though there were 63 sectors per
>track and a whole lot less tracks.
Beware that there are several pitfalls here:

	1) invoking sector translation can have a performance hit.
	   After all, mkfs/fsck -s organises the free list assuming
	   the actual shape of the disc is what you tell it is.
	   These assumptions can go horribly wrong when you invoke
	   peculiar translations like the 1007 can do.  It'll WORK,
	   but you'll have your disc seeking all over the shop.
	   Can you say Sloooooow? I thought you could...

	2) there can be a confusion when you mention 63 sector mode--
	   there is a NON-TRANSLATED 63 sector mode where each sector
	   is 256 bytes in size.  (You did say WD1007 ESDI, right?)
	   You definitely DO NOT want to low-level format the disc
	   in this format :-)

	3) Hey, why muck around? Xenix does *not* have a 1024
	   cylinder limit.  Try it and see--just make sure that
	   in the early part of the disc initialisation process,
	   that you OVERRIDE the disc parameters.  This causes
	   /usr/lib/mkdev/hd to perform a dparam -w which
	   lets you use a disc of any reasonable shape, even if your
	   BIOS does not have a corresponding drive type number.
	   Just use any type number with the same number of heads,
	   and a lower cylinder count to enable the boot sequence
	   to operate properly.  No hassle. Honest. I do it alla time :-)

-- 
Ronald.Khoo@ibmpcug.CO.UK (The IBM PC User Group, PO Box 360, Harrow HA1 4LQ)
Path: ...!ukc!slxsys!ibmpcug!ronald Phone: +44-1-863 1191 Fax: +44-1-863 6095
$Header: /users/ronald/.signature,v 1.1 89/09/03 23:36:16 ronald Exp $ :-)