Re: Can I boot of an XP System disk, nested in a logical volume

A CP/M to XP/P-traveller wrote:

Thank's for your quick response.

We'll that settles it, I'll boot of Partition Magic or some other kind of magic and fix it that-a-way.

Regarding MBR remembering: It's been a long time since I messed with partitions like this, but in the back of my head I have this fragment about boring registry hands-on editing, 'derived Disk ID's' and the 'Master Boot Sector' -- that's S as in 'Senile'. Oddly enough, something as quaint as '4 bytes' and '01B8h' also pop's up, when thinking about it. Any idea?

Yes, that is where the 4 byte long disk signature is held, from offsets 1B8h through 1BBh. I have never ever needed to directly edit this, and I wouldn't ever know how to edit these bytes because they are never the same, as far as I know they are just randomly generated and I haven't a clue how they are arrived at.

These are 4 of the famous 6 bytes that fdisk /mbr rewrites, it rewrites the disk signature at bytes 440 to 443 along with the two bytes 444 & 445. Rewriting the disk signatures allows or causes the Mount Manager to reassign drive letters. The Windows 2000/XP fixmbr command does not rewrite these bytes, it rewrites the first 440 byte and doesn't touch the disk signature, fdisk /mbr rewrites the first 446 bytes and zeros out the signature.

A follow-up on drive letter assignments: Is it possible that a cloned 'XP system disk' could end-up as a 'Blue Screen of Death' -- not knowing which partition it actually belongs to?

Possible I suppose so, but most of the time it will will either go in a reboot loop or boot and give Low Virtual Memory errors messages. One reason for the drive letter change on cloned drives is to keep the parent drive hooked up the first time the clone is booted, being that the clone has the same Mount Manager database, and being that the Mount Manager *always* respects drive letter assignments, it will see the parent drive and its valid disk signature and assign the C: drive letter to the original C: drive, so there will be no C: letter available for the clone. Disconnecting the parent drive the first time the clone is booted will invalidate the Mount Managers drive letter assignment, it will not see a disk corresponding with the signature in its database so it will be able to reassign the now invalid C: drive letter to the clone. After this first boot the old (parent) disk can be hooked up again, the Mount Manager will honour the drive letters of the clone disk and assign different drive letters to the parent disk. This is where fdisk /mbr can repair the drive letter mixup, by rewriting the disk signature it will cause the Mount Manager to reassign drive letters based on its predetermined set of rules.

A final question: Is there an environment variable in XP that tells me where the boot-up actually happens?

I'm not sure that I understand what you mean. Where the "boot-up happens" is determined by ntldr, it determines this by reading the information in the boot.ini file, it will determine the where the boot-up happens when you make your selection at the boot menu, or by using the default= information if you do not make a selection. You may find these interesting:

The PC Boot Process - Windows XP.

Chapter 19 - What Happens When You Start Your Computer

Some of the information in Chapter 19 is a bit dated but the basics all
still apply to Windows XP.


// MPT

"John John" wrote:

See inline for more comments and answers.

First we should make sure that we are on the same page and that we use the same terms else we will all be hopelessly confused! The Microsoft nomenclature defines the following:

*Boot Partition*
The boot partition contains the Windows operating system and its support files. By default, the Windows operating system files are in the WINDOWS folder, and the supporting files are in the WINDOWS\System32 folder. The boot partition can be, but does not have to be, the same as the system partition. There will be one, and only one, system partition, but there will be one boot partition for each operating system in a multi-boot system.

Note On dynamic disks, this is known as the boot volume.

*System Partition*
The system partition refers to the disk volume that contains the hardware-specific files that are needed to start Windows, such as Ntldr, Boot.ini, and The system partition can be, but does not have to be, the same volume as the boot partition.

Note On dynamic disks, this is known as the system volume.

*Logical Drive*
A volume you create within an extended partition on a basic disk. A logical drive can be formatted and assigned a drive letter. Only basic disks can contain logical drives, and a logical drive cannot span multiple disks.

For the purpose of this discussion when referring to basic or MBR disks the terms partition and volume are interchangeable. However, when referring to Dynamic Disks the term volume is solely used, Dynamic Disks do not contain partitions, they contain Dynamic Volumes or Logical Volumes.

A CP/M to XP/P-traveller wrote:

Hi, I'm in a bit of a fix.

I have a non-working Windows XPP-system disc (assigned C:) and I have a clone of that one on a secondary HDD (assigned D:). Non-working, of course. Accoring to support, both C: and D: requires "a bit of registry tweaking" and a Windows 98-startdisk -- using that specific version of /fixmbr. Something that I'm not going to do.

So, in a logical volume, I have a freshly installed, working and active Windows XPP-system disc (assigned E:) -- or at least %SYSTEMROOT% says so. An E-disc I'm hoping to keep as a final C:-disc, if all goes well.

That won't happen. The boot volume must always keep the drive letter assigned to it when Windows was installed. If you want to change the drive letter onto which Windows is installed you must reinstall the operating system. Furthermore, when Windows is installed drive letter assignments are based on the order in which the drives are enumerated and on a predetermined set of rules. Based on the predetermined set of rules a logical drive can practically not or almost never be assigned drive letter C:. Perhaps you mean something else by the term "logical volume", see above for definitions.

Question 1: Can I boot of a logical volume with a system disc (E:) in it?

Once again, we need to make sure that we are using correct terms, see above for definitions. Windows can be installed and booted on a logical volume and the boot volume letter assignment does not matter. The System volume however cannot be a logical volume, it must be an active primary partition.

Question 2: Deleting the C: and D:-discs (primary partitions) won't XPP MBR still 'remember' the then deleted C: and D:-disc, keeping me stuck on a E: assigned-system disc?

The MBR does not store or remember drive letters. Drive letters are stored in the Mount Manager's database. The Mount Manager's database is stored in the registry at:


Keeping the Mount Manager's database in the registry ensures drive letter persistence on NT operating systems. As long as the disk signature remains the same and as long as the drive letter assignments remain in the Mount Manager's database the drives will persistently keep their letter assignment. The point is moot however because the drive letter onto which Windows is installed cannot be changed anyway.

Question 3: Is it possible to *** safely *** convert the logical disc into a bootable dynamic volume, keeping the E:-system disc intact and working?

I assume you mean "basic" disk? Yes, but you cannot have multiple operating systems (multi-boot) on the disk. When you convert the disk to dynamic the partition entries for all but the current Boot and System partitions will be removed.

I might add, I want to keep it as Windows XPP standard as possible; no boot managers or the likes.

It's too late for that, your setup is hardly standard as it is now and it will be barely standard after you convert the disk to dynamic!


And The Windows 2000 Help Files.