*BSD News Article 3764


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From: rommel@Informatik.TU-Muenchen.DE (Kai-Uwe Rommel)
Subject: Re: Another Adaptec Question
References: <7@tama.spec.co.jp> <1992Aug16.144341.24052@Informatik.TU-Muenchen.DE> <15776@star.cs.vu.nl>
Sender: news@Informatik.TU-Muenchen.DE (USENET Newssystem)
Organization: Technische Universitaet Muenchen, Germany
Date: Mon, 17 Aug 1992 17:38:07 GMT
Message-ID: <1992Aug17.173807.2309@Informatik.TU-Muenchen.DE>
Distribution: world,fj,spec
Lines: 54

In article <15776@star.cs.vu.nl> kjb@cs.vu.nl (Kees J. Bot) writes:
>rommel@Informatik.TU-Muenchen.DE (Kai-Uwe Rommel) writes:
>>
>>In article <7@tama.spec.co.jp> amurai@tama.spec.co.jp (Atsushi Murai) writes:
>>>ariticle is not ..but) and Fujitsu M2266SA 1.2 GB Disks. Functionality
>>>is good but it looks like loosing a space about 200MB (above 1Gbyte).
>>>And some guy let me know about this is a known problem of 1542B and
>>>Adaptec will be fixed by new board - 1542C. (Oh well.....)
>>>Now a day, A lot of guys try to run 386BSD with this card without know
>>>this problem!!!
>It has nothing to do with heads, sectors or cylinders.  The group 0 SCSI
>read/write commands allow only for a 21 bit block address limiting one
>to 2 megablocks, which is 1GB at the usual 512 bytes per block.

We don't talk about smart OSes like 386BSD :-) but the original poster
asked why he doesn't see all the space under DOS/Novell. There it has to
do quite a lot with heads/tracks/sectors ...

>The group 1 SCSI read/write commands offer a 32 bit block address
>however, but not all O.S.'s are smart enough to use those commands.
>
>>Adaptec has now a new mapping scheme with 256 heads and 64 sectors per
>>track, [etc...]
>
>At least the 64 sectors per track number is wrong, you can't have more
>than 63 sectors on a track.  I don't like the 256 heads per track
>either, I know of one (1.5GB) disk with an AT interface that uses the
>top 2 head bits for two more cylinder bits.  This limits the number of
>heads per track to 64, but allows for 4096 cylinders.  I don't know if
>this is a normal way of addressing bigger disks under DOS.  Anyone?

Sorry, for those off-by-one errors, here is the original text from the
Adaptec README file:

--quote--
To eliminate the 1 Gigabyte limit, Adaptec's new extended
translation feature uses 255 heads and 63 sectors,
extending the disk drive capacity limit under
DOS to 8 Gigabytes.
--end-quote--

>I do not use the Adaptec BIOS by the way, there is a nice SCSI command
>to ask the drive how big it is and that is all the info you need with
>SCSI.  You can't even see more than two disks with the BIOS.

We may guess how DOS and Novell determine the disk geometry/size ..

Kai Uwe Rommel

/* Kai Uwe Rommel --- rommel@informatik.tu-muenchen.de */

DOS ... is still a real mode only non-reentrant interrupt
handler, and always will be.                -Russell Williams