how to run an operating system on flash drive

NFS I think you are chasing butterflies here mate I personally don't know of any method of carrying around the OS like that only as ISO to install.

I can see what you are getting at but to use any particular Windows OS it needs to be tied to a particular motherboard and just cannot be used on different machines at will.

The only OS that I know that does do this (and there are more I think) is Ubuntu and then you have to use the TRY method see this.

BOOTABLEUBUNTU

Makea bootable Ubuntu disk http://www.ubuntu.com/download

Setthe BIOS to boot from the optical when the machine boots it will show you ascreen with TRY or INSTALL > select TRY. You can of course remove the hard drive and any otherdrives when doing this as if the optical alone is the only drive left in themachine then the BIOS will only find it to boot from.

Whenit is finished - it takes very little time you will get a screen like in thepic .

Openthe drive you want > User and dig down until you get to the data / settingsyou may be able to copy / paste the material you want to an external source orother installed drive doing this.

Iam not sure if it will but I have recovered tons of data etc using this methodboth on "dead" or just plain drives that you cannot get data fromusing Windows.

Um, I run Windows 8.1 from a 16GB USB 3.0 flash drive and it runs fine. Does need a USB 3 port otherwise it is so slow it' unusable.

THIS DOES NOT WORK unless you have a really good, very fast USB 3.0 flash drive. The two Kingstion DataTraveler G4 USB 3.0 drives I picked up don't do it so I ordered a SanDisk Extreme USB 3.0 CZ80 16GB Flash Drive which is supposed to work with WinToGo. Will see when it gets here.

Yup, the SanDisk Extreme works perfectly.

If you would like to have Windows 8/8.1 on a flash drive that you can boot when needed, see here:

[Tutorial]Windows 8 to Go without Enterprise Edition

I believe you can replace Win 8 with Win 7.

I built this on my Windows 8 Pro X64 system.

You can run Linux, Ubuntu whatever off a flash drive

Main Page - Linux Mint

Universal USB Installer ? Easy as 1 2 3 | USB Pen Drive Linux

Rufus - Create bootable USB drives the easy way

Yep Mike I have run Ubuntu in TRY mode for ages now to open up dead or dying drives and to get some net access. The others I have heard of but never have had the need to use them.

USB 2 would I guess not be too slow, since Raspberry PIs can run a Linux OS just fine. You should get LibreOffice Fresh | LibreOffice - Free Office Suite - Fun Project - Fantastic People which is basically free version of MS Office for Linux. Also remember to get a browser like https://www.google.com/intl/en/chrome/browser/ if you don't like Firefox. For the music player, get VideoLAN - VLC media player for Ubuntu. Also, if you are into photo editing, you can get GIMP - Downloads

Of the Microsoft operating systems, only Windows 8 is capable of running from a USB2 or 3 drive. Windows 7 is far too sluggish, and is not worth attempting.

This tutorial is the one to go to for Windows 8:
Windows 8 To Go - Setup on a USB Flash Drive or USB Disk

Here is my version - runs great. USB2 works but is slow at boot and shutdown time. For normal operation it is OK. I recommend to watch the video that is embedded.