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From: wtm@uhura.neoucom.EDU (Bill Mayhew)
Newsgroups: comp.sys.att
Subject: Re: UNIX Formatting Limit
Message-ID: <1991May12.175704.17537@uhura.neoucom.EDU>
Date: 12 May 91 17:57:04 GMT
References: <1991May11.045012.4182@netcom.COM>
Organization: Northeastern Ohio Universities College of Medicine
Lines: 34

Without knowing the specific release of Sys V r4, I can't say for
sure what limited the winchester drive to formatting to only 1024
cylinders.  Most likely the driver is coded with the assumption
that the hardware will have the usual IBM ISA bus limits.  The
original IBM AT disk controller was the WD 1001 which could handle
only 1024 cylinders.  The 1024 cylinder limit is still hard coded
into msdos unless one uses a third party driver such as On Track's
Disk Manager or a smart controller.  There is also a hard limit of
16 heads.

The easiest solution is to use a controller to remap the geometry
of the disk drive to make the drive appear to the operating system
to have a maximum of 1024 cylinders.

I'm using a Priam 330 megabyte ESDI drive on my Sys V r3.2.1 system that
has about 1200 physical cylinders.  The controller I'm using is a
WD 1007 that does sector translation.  I've not had any problems at
all with the arragnement.  I believe that even with the WD 1007,
you're going to be limited to about 504 megabytes of accessible
space by the translation 63 sectors * 16 heads * 1024 cylinders *
512 bytes = 504 megabytes.

There really isn't a good excuse that Sys 4 should not support
large disks on the ISA bus; disks and controllers with huge
geometries have been available for quite some time now.

Bill


-- 
Bill Mayhew      NEOUCOM Computer Services Department
Rootstown, OH  44272-9995  USA    phone: 216-325-2511
wtm@uhura.neoucom.edu   ....!uunet!aablue!neoucom!wtm
via internet: (140.220.001.001)