Inside the Dell Utility Partition

An Exploration by Dan Goodell
Introduction Partition Parameters Sealed State Unsealed State Recreating Customizing
Partition Parameters

The Dell Utility partition is really an ordinary FAT16 partition (type 06h), but the partition descriptor (a 16-byte pointer in the partition table) has been altered to show a partition-type code of DEh instead of 06h (in hexadecimal notation).
(Note to self: the partition-type 0Eh (FAT16X) will work just as well as 06h here. However, to boot the Utility partition the partition itself cannot really be FAT16X because the Dell bios seems to expect the partition will be below cylinder 1024.)
The size of the partition is not critical, and seems to be around 31-64 MB on most systems. The files within the partition typically occupy less than 10 MB of this space.

Although a FAT16 partition would normally be recognizable to Windows, by using a non-standard, unofficial partition-type indicator in the partition descriptor the partition is ignored when Windows is booted from the main partition. This, of course, would be the way Dell likes it -- Dell doesn't want the user to tamper with the Utility partition when using the computer normally. Using any non-standard partition-type indicator will effectively hide a partition like this, but I suppose Dell uses DEh because it's cute (DE = DELL, get it?) and because nobody else is using it.
(Note to reader: the typically accepted method of hiding a 06h or 0Eh partition is to change it to 16h or 1Eh.)
Since DEh is not officially recognized, Dell can design their bios firmware to look for the DEh marker with a reasonable expectation that it will be one of their utility partitions.

The Utility partition is formatted with the FAT16 file system and boots DOS. Older Utility partitions booted MS-DOS 7.0 (the version of DOS from Windows 95). Newer Utility partitions boot DRMK 4.1 or 8.0. DRMK is Dell's own DOS variant, and appears to be functionally similar to MS-DOS.
(Note to reader: the purpose behind developing the DRMK operating system may have been to avoid paying licensing fees to Microsoft, not to add extra DOS functions. DRMK apparently stands for "Dell Real-Mode Kernel".)
Other DOS versions, such as DR-DOS or FreeDOS, may also work just as well here.

The two states of the Utility partition -- sealed and unsealed -- are differentiated by different config.sys and autoexec.bat files. These startup files are designed to automatically follow one of two different scenarios when the partition is booted. The sealed scenario runs the seal.exe program, while the unsealed scenario runs the delldiag.exe program.

author: Dan Goodell