This update resolves an issue that prevents chkdsk.exe from running at system boot. The issue can occur on systems with an IDE drive and is discussed in Microsoft Knowledge Base (KB) Article Q315403. (System Requirements: Windows XP Home / Pro)
When you use volumes that use the NTFS file system on integrated device electronics (IDE) drives with caching enabled, you may receive the following error message during startup:
Unmountable boot device
The normal recovery process in such a case is to run the chkdsk -f command on the computer and continue. However, OEM versions of Windows XP which have the hotfix "Q308402 Cannot Log On to Recovery Console After Running Sysprep in Windows XP" applied, prevent the chkdsk -f command from running.
This is because of the write-pattern optimization in IDE disk drives, the caching routines sometimes write data out of order to keep drive write speeds at the fastest possible level depending on where data is located on the disk. This opens a timing window where the NTFS disk system could have critical tables damaged if a write is not finished.
Microsoft has recommended in the past that caching on IDE drives be turned off on programs with somewhat critical data that is stored on the disk or for situations that allow the slight drop in overall speed. Programs with critical data may need to use SCSI drives, which have better control of data transactions.
News source: Microsoft Windows XP Patch: NTFS chkdsk.exe update
Download: Windows XP Patch: NTFS chkdsk.exe Update - q315403_WXP_SP1_x86_ENU.exe (488kb, 18th February 2002).