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From: Nitezki@NiDat.sub.org (Peter Nitezki)
Subject: Re: SCSI on DOS (was Re: More SyQuest infos)
Message-ID: <1994Nov16.113401.502@nidat.sub.org>
Sender: nitezki@nidat.sub.org
Organization: private site of Peter Nitezki, Kraichtal, Germany
References: <CzAFDt.48r@prz.tu-berlin.de>
Date: Wed, 16 Nov 1994 11:34:01 GMT
Lines: 45

In article <CzAFDt.48r@prz.tu-berlin.de> wolf@prz.tu-berlin.de (Thomas  
Wolfram) writes:
...munch...

> BTW, creating a partition table on the SyQuest media with NeXTSTEP's
> fdisk gives another result then doing it under DOS because NeXTSTEP
> detects 4 heads/17 sectors from the SyQuest drive instead of 64
> heads/32 sectors (with a Adaptec).  It might be that this (4/17
> under NEXTSTEP) could be overridden by making an entry in /etc/disktab.
> 
> Also you should use 'fdisk -useAllSectors /dev/rsd?h' because
> otherwise fdisk limits the access to those sectors "which are
> bios-accessible".  To my knowledge these BIOS limits are 1024
> cylinders, 256 heads and 64 sectors, but NEXTSTEP's fdisk limits
> then partitions to a size of ~20MB - very strange.
> 
> As for DOS: I was told by a SyQuest person that as long as you use
> the SQDRIVER.SYS the translation scheme doesn't matter because the
> driver handles it (there is a additional translation done by it).

Just to give more background info (and not letting pass a chance to rant  
on braindead DOS ;-)

SCSI disks use a linear address scheme that masks the disk geometry.   
Therefore, you never get any problems with exchanging SCSI disks between  
different machines and controllers.  Linear addresses are linear under all  
circumstance.

Domestos (aka MessyDOS) fdisk is supposing to work on geometry aware  
disks.  It addresses cylinders, heads, and sectors like in the old days of  
ST506 and ESDI (and IDE, of course).  SCSI controllers have to destroy the  
linear addressing feature of SCSI in order to support DOS (fdisk)  
partitioning, thus the need for address translation, and/or need a special  
fdisk program.  Therefore, any SCSI disk that got fdisk partitioned lost  
its universal exchangability in the process (By the way, since the address  
translation makes arbitrary choices the optimization features of fdisk and  
format are very likely to turn out as a shot in your foot).  Since NS/FIP  
knows how to work on fdisk partitioned disks (sigh!) there is a danger to  
have unexchangable NS disks, a heavy liability in case of Syquest or any  
similar drives.
-- 
Peter Nitezki      | Nitezki@NiDat.sub.org # Blessed art thou who knoweth
Staarenbergstr. 44 | Tel.:  +49 7251 62495 # not about the pleasure and
D-76703 Kraichtal  | Fax :  +49 7251 69215 # delight of being hooked
GERMANY            |   pgp & NeXTmail ok!  # up to the Net. Peter 1,3-5