RE: fdisk C/H/S IDE drive question


Subject: RE: fdisk C/H/S IDE drive question
From: Jan Zumwalt (jwzumwalt@neatinfo.com)
Date: Sun Feb 08 2004 - 20:16:43 AKST


Here is another possibility...
MS-DOS (actually MS-BIOS) was unable to support drive partitions greater than
about 500mb. Some hard drive manufactures created a work around for problem
by creating a "virtual" sectoring scheme. The drive or controller mediated
calls to the hardware and remapped the sedctor and track calls. This allowed
DOS to think that there was a smaller number of sectors and tracks than
actually existed. By doing this, they allowed DOS to be able to use
partitions as large as 2gb or so (if my memory serves me!).

My guess is that either the controller or hard drive is being shifted to the
legacy DOS support mode and so the "virtual" size is being reported. If you
look directly on the hard drive, a lable should tell you what the "physical"
(true) drive configuration is - then you will be able to tell which
controller is reporting "virtual" size!

Jan Zumwalt

> -----Original Message-----
> From: Andy Firman [SMTP:andy@firman.us]
> Sent: Saturday, February 07, 2004 9:28 AM
> To: aklug@aklug.org
> Subject: fdisk C/H/S IDE drive question
>
> I have 2 WD400BB 40GB drives and getting ready
> to start software RAID on a new system.
>
> Motherboard is a simple MSI KM4M with 2 IDE controllers.
>
> This is strange to me:
>
> fdisk reports this when either drive is /dev/hda
> Size: 40020664320 bytes
> Heads: 255 Sectors per Track: 63 Cylinders: 4865
>
> fdisk reports this when either drive is /dev/hdc
> Size: 40020664320 bytes
> Heads: 16 Sectors per Track: 63 Cylinders: 77545
>
> man fdisk says Linux never uses CHS but I would like
> to know why fdisk reports things differently when the
> drives are on different IDE controllers.
>
> When I go into the BIOS, it shows both drives being
> exactly the same in all aspects.
>
> Both drives are set to "auto" in the bios and they
> both have the jumper on CS (cable select)
>
> Why would fdisk report differently when the drives
> are on the second IDE controller?
>
> Must be some sort of motherboard/bios issue right?
>
> Thanks,
> Andy
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