OT: question about booting OS from USB

I don't know about various Linux distributions but AFAIK Windows will not run off a USB drive. it may be possible to do a bunch of tricks to accomplish it but it isn't normal.

IMO, if you don't want dual/mutliple boot systems, and want a removable drive the best way to do it is with a rack/caddy. Lot faster too.

That's what I thought too, the only way I know to boot off of an external drive is with an eSATA connection, not USB. But people can boot utilities from USB memory sticks, so I was wondering if there's a similar trick to put something on the external drive to make it operate like a big USB stick. But also there's a difference between running some utility that gets loaded into RAM vs. running a complete OS, so I'm guessing its not possible but it doesn't hurt to ask.

I'm also assuming if I can't actually boot from a USB drive then there's probably no risk in leaving the C: partition marked as active (boot) either, but would rather ask first as opposed to just try it and find it has some unpleasant side effects. Most likely I'll just turn it into one big partition and reformat for backup storage. If I ever need to replace the main drive I don't really need instant swap capability anyway, I'll have time to plug the external disk back in and restore my entire system to it from backups (I have multiple backup drives).

If the partition on the USB drive is Active and the MBR contains valid "booting" code and you try to boot the USB drive, it will error and stop. You can remove the Active flag if you want, but it won't hurt anything. Normally, if you have at least one Primary partition on a drive, one of them will be set Active.

Any legal issues aside, booting Windows (I've only done it with XP) from a USB drive is not worth the trouble (in my opinion). The speed is terrible (especially on flashdrives) and it won't move easily from one computer to another. The only real purpose I've seen for this is to have a "duplicate" Windows ready to boot when another internal drive is unavailable and down-time isn't possible. Most of the time, people who ask this want to create "their Windows" on a USB drive and be able to take it with them and use it on whatever computer they're at (as a Live OS). Windows won't work well like that, if at all.

Linux is usually more flexible and may run just fine from your USB drive. Just be aware that Linux can also be "broken" by drives changing (boot order, drives connected/disconnected, etc.).

"If the partition on the USB drive is Active and the MBR contains valid "booting" code and you try to boot the USB drive, it will error and stop..... Linux is usually more flexible and may run just fine from your USB drive."

Is this a security issue with Windows wanting to limit the portability of any given copy of their OS??

I am able to easily boot Ubuntu using GRUB on my USB drive, but I haven't tried setting that drive up as dual-boot yet. Have you ever tried that particular configuration, starting Vista from GRUB on a dual-boot setup on a USB drive?? I'm guessing I have nothing to risk by trying, if it just halts it shouldn't do any damage to the rest of my system, right??

When I tried to boot Vista from GRUB it complained about ntldr being missing. I suspect that had to do with the internal drive (where my Vista installation resides) not being visible at boot time, so GRUB couldn't find the partition it was expecting to launch Vista from. GRUB found that Vista installation when I installed Ubuntu, and added it to the startup list, so I'm assuming it knew which drive/partition to point to. Or would the error I saw be caused by something else??

Now, supposing I add Vista to the USB drive and get it to dual-boot over USB, my next concern is having two windows partitions with the active flag set. If the USB drive can't see the internal drive during boot, and vice-versa, then as long as I get through the boot stage without anybody seeing the second active flag I think its OK after that, right??

Update: Did another Linux install, this time with GRUB2, and now I can boot both linux (installed on the USB drive) and Vista (installed on the internal drive) from GRUB using a USB drive. But when I tried to install Vista on the USB drive and boot it from GRUB, it got partway through the boot process, then crashed right after the file system checks. I assume that was what Mudcrab was talking about in his reply.

I was hoping to be able to boot Vista through GRUB on a USB drive to create an alternative to the Acronis boot disk, which as everyone knows is somewhat flaky when it comes to detecting various hard drives in your system. If I could boot Vista on USB then restoring the internal hard drive system partition could be done "while running windows" on the USB drive, eliminating the need for the Acronis boot disk.

If anyone else has any experience with getting this type of configuration to work I'd like to hear about it.

You can always boot a USB drive with Grub4DOS loading WinPE ISO with TI. I did this until moving to a secondary internal drive that I boot via BIOS into Grub4DOS to load a variety of ISOs or a second Windows XP system.