Windows XP bootup

[Lonyo]

Here's a quick rundown of a problem I just had:

Had 5 harddrives.
PATA1: HDD Master, HDD slave
PATA2: CD Master, HDD slave
SATA1 & 4: HDDs

Windows (XP, SP2) was installed to a PATA drive which was hooked up as slave (Can't remember if it was channel 1 or 2)
I removed 1 SATA drive and both PATA master drives, leaving Windows drive and SATA1.
Windows then proceeded to give me boot drive errors and would not boot from the PATA HDD with Windows on it. Drive was detected fine etc.
I tried the drive on both channels and as master and slave, still no luck.

I installed my new SATA HDD and took the PATA out (so now I have 2 SATA drives again), and began installing Windows to that drive.
After Windows was installed to the new SATA drive, I added back the PATA drive.

Windows then booted straight to the PATA install of Windows. Didn't even give me a boot menu to choose between the two.

Why did my PATA install suddenly come back? Does Windows put something on another drive if the Windows drive is installed as slave on a channel?
I seriously tried everything to boot from the PATA and it would not play ball at all. I even tried a fixmbr in the recovery console, and no dice.

It wasn't until I installed a fresh copy of Windows to another drive that it suddenly decided to work again.


The problem has seemingly sorted itself out, but I was wondering if there was a real explanation as to what exactly happened.
Did one of the drives I removed contain something essential to getting Windows to boot?

 

[Billb2]

I think you're confusing boot drive (the drive set as the boot device in the BIOS when the Os was installed) and the drive where the Windows folder resides (the drive to which you installed Windows).

The BIOS boot drive gets the boot sector (the first sector, where the boot files are installed), MFT, and boot files. The Windows folder contains the windows programs/drivers/etc that windows uses to boot.

If the post routine does not find a bootable first sector on the drive set as the boot drive in the BIOS (or if that drive is not an active, primary drive or partition) it starts looking elsewhere for a drive/partition with a bootable first sector and boots the first one it finds. Putting drives on different ports and/or, adding/removing drives will effect the results of this searching.