Maybe I can make my point clearer:
You own machine A, it’s a Dell Pentium 4 - 2Ghz, ATI card, and Intel motherboard. You set up a removable drive bay, load a Maxtor 40GB hard drive in the tray, set as master on the primary IDE chain.
You set up windows XP, do all the patches and service packs, Office, and other programs, everything works swell.
Your friend owns machine B, a HP AthlonXP 2000, Nvidia card, AMD motherboard. You install a removable drive bay in this machine and bring your tray with the Maxtor 40GB over, with the intention of booting the machine with your copy of windows XP.
Put the drive in, turn the key lock, push the power button and viola!! BSOD (blue screen of death). Why? Well, in the case of NT, (or 2K or XP) it’s the IDE driver. The one installed for your Intel motherboard won’t have a chance in hell on the AMD VIA IDE chipset. And so it goes down the line, if it wasn’t the chipset it woulda been the video drivers, the motherboard resources etc…
Now, say you have machine A, you have the OS installed on an internal 40GB Maxtor HDD set as the master on your primary IDE chain, and install the removable bay as the slave on your primary chain. You mount a Seagate 80GB in the removable tray and slide it into your new bay. You store all your MP3s and videos and other data type files on the removable drive (probably shows up as ‘D’ in windows explorer) with the intention of bringing it over to your buddies. Slide the tray out; mosey over to your friend with the HP machine. Install a removable drive bay on his machine as the slave on the primary chain, or even the slave on the secondary IDE chain, slide the drive tray in and power up. As long as his BIOS is set to auto detect (and most newer machines are), you should find a new drive in windows explorer, with all your fun stuff on it.
Now, there are a few caveats:
As said above, windows 9x (95,98,Me) can sometimes be more tolerant of odd hardware all of a sudden appearing, so you can be successful sharing one system drive between 2 hardware boxes. I wouldn’t count on it reliably though.
If machine A is XP (or NT or 2K) the drive is probably formatted using a file system called ‘NTFS’, which any 9x (95,98,Me) system will not be able to read. So even if it’s a secondary drive in machine A and you pop it in as a secondary on machine B, and machine B is 98, windows is going to claim the drive is not formatted, would you like to format now? You need to say NO; otherwise you’re going to completely erase the contents of that drive. Going the other way will work though. If machine A is 98 and you pop out that secondary drive (which is most likely formatted as ‘FAT32’) to put in machine B, which is XP, It should read the drive no problem. XP can read NTFS, FAT16 and FAT32.
If you have programs on your removable drive, don’t count on them to run properly when you put the drive in machine B. There is usually stuff installed on the system drive that the programs you installed on the removable depend on. Might work, might not.
Your best bets for removable drives is either:
One bay mounted in one machine, two trays, a unique OS on each.
2 bays mounted as ‘slave’ or secondary’ drive positions in different machines, with the intention of ONLY sharing data type files. (Watch out for compatible file systems)