Notes on Installing Hard Drives Larger Than 2 Gigabytes

Filename: OVER2GB.TXT
WWW URL:  http://www.firmware.com/support/bios/over2gb.htm
FTP URL:  ftp://ftp.firmware.com/text/over2gb.txt
Revision: 03/10/97  TLS  Micro Firmware Technical Support
Summary:  Many BIOSes, including older versions of Micro Firmware
          upgrades based on Phoenix 4.03 code, do not support large
          drives over 2GB. This file indicates which versions of
          our upgrades do and don't support drives over 2GB.

The Micro Firmware BIOS upgrades based on 4.03 code do not natively support drives larger than 2 GB. This is due to a bug in which not enough bits in CMOS RAM are being used to store the cylinder number. This bug did not become apparent until drives larger than 2 GB became available. We became aware of this problem on 04/11/96 and immediately began investigating and correcting it.

A hard drive larger than 2GB may autotype at its correct factory parameters but CMOS will not hold those values. The cylinder field is limited to 4095 even though larger values may appear here when a drive is autotyped. We are revising all of our 4.03 BIOS upgrades to support drives up to 8GB as advertised, and free updates will be made available to our customers upon request.

None of our 4.05 upgrades (HS series) have this problem.

Here is a breakdown of all of our 4.03 upgrades:

Part no.      Version needed to support drives over 2GB

I4GS10        4.03.6.08 Released 06/28/96 (or move to I4HS10)
M3GS20        4.03.6.09 Released 02/04/97
M3GS30        4.03.6.09 Released 08/05/96
M4GS20        4.03.6.07 Released 04/17/96
M4GS25        4.03.6.13 Released 04/17/96
M4GS30        4.03.6.14 Released 02/26/97
M4GS45        4.03.6.07 Released 04/25/96 (or move to M4HS45)
M4GS45G       4.03.6.08 Released 06/20/96 (or move to M4HS45G)
M4GS45GP      4.03.6.08 Released 04/25/96 (or move to M4HS45GP)
M4GS50        (will not be updated - move to M4HS50)

Also note that DOS is limited to 2GB per partition or logical drive, so a 2.5 GB drive must be partitioned into at least two drives.

A temporary solution to the BIOS limitation is to just set the drive up as 4095 cylinders, 16 heads, 63 sectors and use it as a 2GB drive. This will, however, require that all data be backed up prior to reconfiguring, repartitioning, and reformatting the drive once the BIOS is updated. The Western Digital AC32500 ships with EZ-Drive, which can also be used as a temporary solution, and will also require repartitioning and reformatting to set the drive up properly. A better solution may be to hold off on installing the 2.5 GB drive until obtaining from us the revision that is needed to set the drive up properly.

In case precise numbers are needed - the limitation is actually 2,113,413,120 bytes, which is 2.1GB or 2113MB, if we define a megabyte as 1,000,000 bytes (as the drive manufacturers do), or 2GB or 2015MB, if we define a megabyte as 1,048,576 bytes (as FDISK does).

This is the first 2.5GB IDE hard drive to appear on the market (March/April,1996).

The factory parameters are 4960 cylinders x 16 heads x 63 sectors.

The plate on top of the drive shows an alternate set of jumper settings which are to be used only in a certain condition. The documentation explains that the only condition under which these alternate jumper settings are used is when a BIOS is not only limited to drives smaller than 2GB but also has no User Definable drive type setting. So we should not have to use the extra jumper with any of the Gateway 2000 systems that the upgrades in the chart above are for. This drive should be jumpered just like all other Western Digital Caviar drives. The alternate jumper settings cause this drive to report its parameters as 4092 x 16 x 63.