Filename: W95PARTN.TXT
WWW URL: http://www.firmware.com/support/bios/w95partn.htm
FTP URL: ftp://ftp.firmware.com/text/w95partn.txt
Revision: 02/04/99 TLS Micro Firmware Technical Support
Summary: WIN95 FDISK may use new partition types which makes drive
unaccessible by DOS 6.x and may also cause "phantom" drives
and data loss.
1 - WIN95 FDISK Shows PRI or EXT DOS Partition, DOS 6.x Shows NON-DOS
Windows 95's FDISK can use 2 new partition types - type 0Eh (Primary DOS) and type 0Fh (extended DOS). WIN95 FDISK will use these partition types only under these circumstances - (1) the drive supports LBA, (2) the BIOS supports LBA when communicating with the drive, and (3) the BIOS supports INT13 Extensions (which allows LBA support on the software side of the BIOS). Most modern IDE or EIDE hard drives over 500MB support LBA. Phoenix BIOSes support LBA starting with version 4.03 of the base code. Phoenix BIOSes support INT13 extensions starting with version 4.04 of the base code. See our article titled "Notes on LBA" ( http://www.firmware.com/pb4ts/lba.htm ) for more information on LBA and INT13 extensions. These new partition types are mentioned in a Microsoft KnowledgeBase article - Q69912 - "MS-DOS Partitioning Summary". This article can be found at this URL: http://support.microsoft.com/support/kb/articles/q69/9/12.asp
If WIN95 assigns type E or type F to a partition, it will not be accessible by any DOS version prior to DOS 7 (WIN95 DOS). FDISK from MS-DOS 6.22 or earlier will show such partitions as NON-DOS.
This problem can be prevented or solved in 2 ways - (1) partition the drive with DOS 6.x FDISK and then install or reinstall WIN95, or (2) use the /X parameter with WIN95's FDISK, which will prevent it from using types E and F. In either case, type 6 will be used instead of type E for a Primary DOS partition and type 5 will be used instead of type F for an Extended DOS partition. This may possibly cause some performance loss on the drive. There may be no reason why some systems need to be accessed with older DOS versions, in which case this would not be a reason to remove or prevent the use of the new partition types. However, there are other problems that can be caused when these partition types are used. This is described in the following section.
2 - "Phantom" Drives and Potential for Massive Data Corruption
Upon investigating calls from some of our customers reporting extra drive letters and duplicate drives under Windows 95, we discovered some problems caused by a bug in the way that WIN95 was handling drives that were assigned the new partition types.
Problems such as extra drive letters, duplicate drives, and data corruption can occur under certain circumstances. This may be limited to drives that have been partitioned into primary and extended partitions and seems to be associated with switching between WIN95 and MS-DOS mode.
We contacted Microsoft in March of 1996 and were told that they were already aware of this problem and that it would be addressed soon. Shortly thereafter, an article explaining the problem appeared in the Microsoft KnowledgeBase - Q148821 - "Possible Data Loss with LBA and INT13 Extensions". This article can be found at this URL: http://www.microsoft.com/kb/articles/q148/8/21.htm A replacement driver to fix the problem appeared on Microsoft's web site on June 27, 1996. DSKTSUPD.EXE can be obtained at this URL - http://www.microsoft.com/kb/softlib/mslfiles/DSKTSUPD.EXE This file will automatically update the driver DISKTSD.VXD in the WINDOWS\SYSTEM\IOSUBSYS directory. Old version of DISKTSD.VXD is 16478 bytes, dated 7-11-95 9:50a, new version is 16514 bytes, dated 3-22-96 9:52a.
These problems can also be prevented by using DOS 6.22 (or earlier) FDISK to partition hard drives prior to installing WIN95 or by using the /X parameter with WIN95's FDISK, which will prevent it from assigning type E or F to any partitions.
Note - the original version of this article was much longer, containing details on how we duplicated the problem and DEBUG scripts to check and change partition types. This article is still available to anyone interested in additional details at this URL - http://www.firmware.com/pb4ts/w95fdisk.htm or on our FTP site as W95FDISK.TXT.