Filename: OVER8GB.TXT
WWW URL: http://www.firmware.com/support/bios/over8gb.htm
FTP URL: ftp://ftp.firmware.com/text/over8gb.txt
Revision: 06/29/99 TLS Micro Firmware Technical Support
Summary: Discusses issues with setting up hard drives over 8GB and
tells what revision level of each of our BIOS upgrades is
needed to support drives over 8.4 GB.
Until around 1994, the BIOSes on most PCs were limited to 504MB hard drives. Newer BIOSes correct this limitation and theoretically work with hard drives up to 8.4GB. In early 1996 the first IDE drives larger than 2.1GB became available. At this time it was discovered that many BIOSes were unable to handle hard drives over 2.1GB. Many systems with relatively modern BIOSes still have this limitation. This has to do with not enough space being allocated in CMOS RAM to store the value for cylinders over a certain size. Our text file OVER2GB.TXT discusses this issue. This file is available on our web site at this URL: http://www.firmware.com/support/bios/over2gb.htm
Many Phoenix 4.03 and 4.04 BIOSes are limited to 3.2GB hard drives. None of our BIOS upgrades have this problem. See OVER3GB.TXT for more information on this problem. This file is available on our web site at this URL: http://www.firmware.com/support/bios/over3gb.htm
The first IDE drives larger than 4.2GB appeared on the market in early 1997. These drives seem to work OK in some systems and not in others. This problem is not due to a bug in the BIOS but is actually an operating system issue, pertaining to all versions of MS-DOS through 6.22. Windows 95 seems to have the same problem. The problem is that DOS cannot handle a translated drive geometry with 256 heads. Although this is an operating system limitation, it appears that the appropriate way to deal with this problem is to account for it in the system BIOS. Our text file, OVER4GB.TXT, discusses this issue. This file is available on our web site at this URL: http://www.firmware.com/support/bios/over4gb.htm
As of 03/21/97, all of our BIOS upgrades support drives up to 8.4GB.
The 8.4GB limitation is both a BIOS issue and an operating system issue. For the BIOS to support drives over 8.4GB, the BIOS must include INT13 Extensions, which is a new set of BIOS calls. Some BIOSes that do include INT13 Extensions do not include specific support for drives over 8.4GB.
MS-DOS 6.22 is limited to 8.4GB drives. This cannot be corrected by a BIOS upgrade or BIOS extension. If a drive larger than 8.4GB is partitioned with DOS FDISK, it will be limited to 8.4GB.
All versions of Windows 95 support drives larger than 8.4GB. However, the system BIOS must correctly handle these drives. Very few BIOSes dated earlier than 1998 will correctly handle drives over 8.4 GB.
See http://www.firmware.com/support/bios/fdisk.htm for more details on WIN95/98 FDISK.
We have revised most of our 486 and Pentium BIOS upgrades to handle hard drives larger than 8.4GB. A few have not yet been revised or have not yet been tested and released. Most likely, we will not update the 386 upgrades and some of the older 486 upgrades based on 4.03 code.
The following chart will be revised as needed to indicate which version of each of our upgrades has been revised to support drives over 8.4 GB.
Part No. Version Needed for Date Released
Drives Over 8.4 GBI4HS10 4.05.10 03/27/98 I5HS10 4.05.07 - not yet tested I5HS15 4.05.19 04/19/99 I5HS20 4.05.29 03/10/98 I5HS25 4.05.16 02/18/98 I5HS30 4.05.09 02/11/98 I5HS35 all revisions support over 8.4GB I5JS40 all revisions support over 8.4GB I5JS45 all revisions support over 8.4GB M3GS20 no plans to revise for over 8GB M3GS30 no plans to revise for over 8GB M4GS20 no plans to revise for over 8GB M4GS25 no plans to revise for over 8GB M4GS30 no plans to revise for over 8GB M4HS45 4.05.19 04/09/99 M4HS45G(P) 4.05.17 08/31/98 M4HS45GC 4.05.10 - not yet tested (low priority) M4HS50 4.05.13 - currently being tested (06/99) M4HS60 no plans to revise for over 8.4GB M5HS10 4.05.18 04/14/98 M5HS15 4.05.10 05/13/98 M5HS20 4.05.05 02/25/98 M5HS60 4.05.26 04/09/99 P4HS00 no plans to revise for over 8.4GB P4HS10 4.05.22 11/18/98 P4HS20 4.05.10 02/17/99
NOTE - In some cases, there may be revisions listed above that are later than the minimum revision needed for 8.4GB support. This is because we are constanty revising all of our parts and we may sometimes provide an unreleased beta version to a customer who needs a feature such as support for larger drives. The released revisions listed above may also have been superceded by newer released revisions. We keep update versions of all of our flash BIOSes on our website so that our customers can always update to the current released revision.
These updates can be found here:
http://www.firmware.com/support/updates/
Hard drives over 8.4GB are supposed to report their CHS geometry as 16383 x 16 x 63.
In all of our upgrades that support drives only up to 8.4 GB, larger drives should autotype in CMOS setup to CHS values of 16383 cylinders, 16 heads, and 63 sectors and show a size of 8455MB. Some drives may behave differently.
In our 4.05 BIOS upgrades that do support drives over 8.4GB, the CHS values shown in CMOS when the drive is autotyped are calculated from the total drive size.
In our BIOS upgrades based on Phoenix 4.0 Release 6.0 code, hard drives over 8.4GB should show cylinder, head and sector values in CMOS as reported by the drive when set to auto. The correct total drive size should be shown.