Inside the Dell PC Restore Partition

An Exploration by Dan Goodell
How the DSR Partition Boots

All DSR versions boot by using MBR boot code that is new and customized by Dell. This Dell MBR does not affect the boot process when booting the Windows partition or the Utility partition--indeed, no special MBR is needed to boot either of those. However, the DSR partition cannot be booted without this new MBR.

To reach the DSR partition, Ctrl+F11 must be pressed when the computer begins to boot. A normal MBR does not contain any provision for recognizing the Ctrl+F11 key combination, so would simply ignore the keys and boot normally. Dell's new MBR code, however, recognizes Ctrl+F11 and diverts the boot process to the DSR partition (typically, "PBR 3"). The Dell MBR displays a characteristic single blue line on a black screen during the boot process. A normal MBR will not show this blue line, so that is an indicator that can be used to tell whether or not your system has a functioning Dell MBR.



The Normal Boot Process

The boot process begins with the machine's Power-On Self Test (aka, "POST"), during which the screen normally displays the large, familiar blue DELL logo on a black background, with a white progress bar in the lower center. During POST the bios is surveying and testing what devices are connected. If it sees a key pressed down when it surveys the keyboard, it assumes you have a stuck key and displays a "keyboard error" message. This means that keys pressed too early are not registered and just serve to annoy the bios test.

When the keyboard-test phase of POST is completed the F2 & F12 prompts will appear in the upper right corner of the screen. You won't see those prompts until the bios has finished testing the keyboard. The keyboard's caps-lock, num-lock, and scroll-lock leds are flashed on-off during the keyboard test, so the blinking leds are another clue as to when keypresses will start being accepted and queued.

When POST finishes, the Dell logo disappears and is replaced by a black screen. The Dell MBR inserts a single blue bar at the top of this black screen, with "www.dell.com" in white-on-blue text. This blue bar will pause for exactly 2.0 seconds before reading the keyboard buffer to see if any keypresses are in the queue. (The 2000-millisecond pause is actually programmed into the MBR code, so this is not an approximate number.)

To divert the boot process to the DSR partition, press down the Ctrl key, press down the F11 key, then release both keys together. The keys must be pressed after the appearance of the F2/F12 prompts and before the end of the blue-bar's 2-second pause.

If the Ctrl+F11 keys are waiting in the buffer at the end of the 2-second pause, the boot process is diverted. If not, the normal boot process continues: the MBR searches the partition table for the 'active boot' flag and boots that partition. Normally, this is the NTFS (type '07') Windows partition, and you'll next see the familiar Windows XP splash screen.

(Note to reader: some users have trouble seeing the blue bar. In some cases, a monitor that has just been turned on may not warm up soon enough to show what's on the screen, so the user may miss the blue bar. In other cases, a misaligned monitor may not be adjusted properly for the text-mode screen, and the blue bar may actually be off the viewable area beyond the top edge of the screen.)

When the computer is operating normally, the FAT16 Utility partition is marked with a 'DE' partition-type indicator, the main Windows partition is '07' (NTFS) and active, and the DSR partition bears a 'DB' indicator. The DSR partition itself is really a FAT32X partition with the partition-type byte in the partition table changed to DBh.    (Note to reader: '06' is the normal indicator for a FAT16 partition, and '0C' is the normal indicator for FAT32X.)


The PC-Restore Boot Process

If the Ctrl+F11 keys are waiting in the buffer at the end of the 2-second pause, the boot process is diverted. The MBR searches the partition table for a partition of type 'DB', changes it to '0C' (the code for a normal FAT32X partition), marks the partition 'active', and then boots that partition. The DSR partition becomes drive C: when it boots, and operates as a normal FAT32 DOS partition.

(Note to self: The Utility partition boot process moves on to the active partition if no 'DE' if found. In contrast, if the Restore process doesn't find 'DB' it hangs with a simple "Cannot restore" message. Examination of the boot code suggests the system may be left with no active partition following a failed attempt to boot the DSR partition.)

Because the DSR partition is FAT32, it boots to a FAT32-aware operating system. Early versions of the DSR partition boot either DOS or DRMK, which are 16-bit operating systems. The latest DSR versions boot a WinPE 32-bit operating system.

The use of this specialized MBR has significant ramifications. Disk overlays such as Ontrack Disk Manager, EZ-Bios, or Go-Back are incompatible with the Dell MBR. Multiboot managers that install themselves in the MBR will render the computer incapable of subsequently booting the DSR partition. Installing Windows from a Windows installation CD and the usual methods of restoring the MBR--e.g., "fixmbr" or "fdisk /mbr"--will also break Dell's PC Restore ability.


author: Dan Goodell

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