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From: bmarsh@cod.NOSC.MIL (William C. Marsh)
Newsgroups: comp.os.msdos.misc
Subject: Re: Max cylinder in DOS 4.01?
Keywords: DOS 4.01
Message-ID: <2086@cod.NOSC.MIL>
Date: 30 Aug 90 19:43:47 GMT
References: <11478@cs.utexas.edu> <1742@io.UUCP> <145@thor.UUCP>
Reply-To: bmarsh@cod.nosc.mil.UUCP (William C. Marsh)
Distribution: usa
Organization: Naval Ocean Systems Center, San Diego
Lines: 26

In article <145@thor.UUCP> scjones@thor.UUCP (Larry Jones) writes:
>In article <1742@io.UUCP>, prs@io.UUCP (Paul Schmidt) writes:
>> 1024 is the maximum number of cylinders a standard, compatible _BIOS_
>> can handle. With the appropriate device drivers, I should think that
>> virtually any version of DOS could handle larger drives. I expect that
>> when you purchase a large drive, that the supplier should provide a
>> compatible device driver.
>
>Rumor has it that the next release of DOS after 5.0 will provide
>support for disk with more than 1024 cylinders.

I can't see how this could be accomplished, since the BIOS interface is
limited to 10 bits for cylinder address (and, for that matter, the WD1003
chip set had the same limitation)

It is the controller manufacturer who needs to provide the driver/support
for more than 1024 cylinders.  With sector mapping, WD, Adaptec, and DTC
support more cylinders, but even with sector mapping this still leaves a
maximum of 512M per drive.

Bill
-- 
Bill Marsh, Naval Ocean Systems Center, San Diego, CA
{arpa,mil}net: bmarsh@cod.nosc.mil
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"If everything seems to be coming your way, you're probably in the wrong lane."