Inside the Dell Utility Partition

An Exploration by Dan Goodell
Unsealed State

Once the Utility partition has changed into its unsealed state, it is no longer the active partition. The computer will boot directly into Windows unless the user deliberately opts to boot the Utility partition from the bios boot menu. The key combination to do this varies from one machine to the next. On this test Dimension 4600, pressing F12 during POST (Power-On System Test) when the computer is turned on will bring up a bios boot menu, from which the user can select to boot the Utility Partition. When selected, the bios routine scans the partition table for a partition of type DEh. If found, it boots that partition, disregarding which partition is marked active in the partition table. If no DEh is found, it bails without displaying any error message and proceeds to boot the active partition instead.

When the Utility partition is booted from the bios boot menu, it's interesting to note that nothing actually changes in the partition table. The Utility partition is still DEh and the Windows partition is still marked active. The bios actually copies the disk partition table into ram and then uses it like the real partition table. The partition-type is changed from DEh to 06h and the partition is marked active -- all in the ram copy. Then the bios transfers control to the active partition in the ram copy.

I have experimentally determined that the bios menu does not require the Utility partition to be the first partition on the disk, nor does it have to be the first partition listed in the partition table.    (Note to reader: In case the reader doesn't know this, these are two different things -- the order the partitions are listed in the partition table does not necessarily have to correspond with the order of the physical partitions on the disk.)    However, in order for the Dell bios to be able to boot it, the Utility partition does have to be within the first 8GB of the disk.

Having been replaced by seal.exe when the system was unsealed, the new config.sys and autoexec.bat automatically launches delldiag.exe, the Dell Diagnostic utility program. When delldiag.exe exits, dellboot.exe is automatically executed and reboots the computer.

Warning: Although the Utility partition does not need to be the first partition for it to function, there are practical reasons for keeping it in the first position.

If the computer is equipped with a Dell PC-Restore partition, that feature requires the Utility partition to be first -- not for the Utility partition to function, but for the PC-Restore partition to function correctly.    (Note to self: I haven't determined if the same restriction is imposed by seal.exe.)   

Also, version upgrades to the Dell Diagnostics utility are sometimes available for some models. These upgrades may be supplied in a variety of formats, with one format (since perhaps 2007?) being a 32-bit executable that updates the Utility partition from Windows. A user has reported that these Windows versions seem to require that the Utility partition be first or the update will not proceed.

author: Dan Goodell