*BSD News Article 38147


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From: wolf@prz.tu-berlin.de (Thomas Wolfram)
Subject: Re: SCSI on DOS (was Re: More SyQuest infos)
Sender: news@prz.tu-berlin.de (Newsadmin Elwood-PRZ)
Message-ID: <CzKz23.7rz@prz.tu-berlin.de>
Date: Sun, 20 Nov 1994 19:20:25 GMT
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References: <CzAFDt.48r@prz.tu-berlin.de> <1994Nov16.113401.502@nidat.sub.org>
Organization: PRZ TU-Berlin
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Followup-To: comp.sys.ibm.pc.hardware.storage,comp.periphs.scsi,comp.sys.next.hardware,comp.os.linux.misc,comp.os.linux.help,comp.os.386bsd.misc,comp.os.386bsd.questions

Hi,

Peter Nitezki (Nitezki@NiDat.sub.org) wrote:

[...]

> 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.

Unfortunatly true, but fdisk partition tables contain not only
the partition locations in cylinder/head/sector specs but as
well as in absolute sector specs (starting sector and size)!

So smart system/driver devlopers could choose these entries
to locate the respective partitions on the removable media.
Should be no problem (i.e. naturally) on non-DOS systems to
just ignore the pseudo-physical specs in the fdisk partition
table. Even the DOS file system doesn't use the c/h/s
(except of some not-used entries in the DOS-boot sector)
but clusters (linear addressed!), as far as I know.

To my mind that should be possible also for fixed disks.
Or why not? 

Thomas
--
Thomas Wolfram        <thomas@aeon.in-berlin.de>    Germany:    0 30 31421171
PRZ TU Berlin         <wolf@prz.tu-berlin.de>        abroad:  +49 30 31421171
EANTC                 WWW:                 http://www.prz.tu-berlin.de:/~wolf
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