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HungryGuy's avatar

How do I boot from an external USB drive (not a thumb drive)?

Asked by HungryGuy (16014points) June 1st, 2010

I bought a new PC recently, which came with Windows 7 pre-installed. I want to run Linux, but I don’t want to just throw away Windows because (1) I paid for it when I bought the PC, and (2) it might be useful to have around on occasion. I had planned to install a swappable drive bay, but that plan was thwarted by the design of the computer that the drive bays are behind little spring doors. And since Windows is already installed, it’s too late to partition the drive and set up a dual-boot scheme (and I’m afraid I’ll run afoul of Microsoft’s copy protection if I uninstalled it and tried to reinstall it). So now my plan is to install Linux on an external USB hard drive (a real drive, not a thumb drive). So is it possible to boot from an external USB drive?

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7 Answers

Rarebear's avatar

You’ll need to go into your BIOS and tell it which drive to boot from.

the100thmonkey's avatar

You can usually select the boot device by holding down one of the F keys during POST. You will usually see a message telling you to “press F* for boot options”, that’s what you want to do.

However, it’s quite possible to install Linux on the internal drive – Ubuntu (and all other distros in fact) give you the option of resizing the partition(s) on the primary drive during install. This lets you install Linux into the empty space you created. Ubuntu will then write GRUB (its bootloader) to the MBR of the primary drive. This will allow you to choose which OS to boot into when you turn the PC on. This method holds a big performance advantage over external drives, which are limited by the bandwidth of the bus – USB 2.0 is limited to 480mbps, or about 26MB/s theoretical bandwidth. A SATA-2 drive has a theoretical bandwidth of 3gbps, or ~300MB/s. Of course, standard HDDs don’t actually reach those speeds, but they’re a lot faster than USB externals.

If you’re worried about buggering the install/partition table up (very unlikely, but it could conceivably happen), then I’d recommend making an image of the untouched drive using P.I.N.G. and saving that to an external USB drive. If there are any problems, you can just boot into PING again and restore the original Win7 image.


HungryGuy's avatar

Thanks to both of you. I’d already used the BIOS over the weekend to change the boot sequence so that I can boot DOS from the floppy drive. But booting from a USB drive doesn’t seem to be one of the options.

Rarebear's avatar

@HungryGuy That’s weird. I have a PC and it will actually automatically try to boot from my external hard drive unless it’s turned off (I never bothered to change the settings). You might want to double check that.

the100thmonkey's avatar

Some BIOSes don’t have the option to boot from USB drives.

Does the PC have eSATA connectors?

HungryGuy's avatar

@the100thmonkey – Not on the outside. That would have been great had it had an external SATA connector, eh? But, hold that thought! Maybe I can get a long SATA cable and thread it through an unused bay in the front of the case. Then just change boot order in the BIOS for whichever OS I want to run…

the100thmonkey's avatar

That will work, but don’t forget the power connector!

SATA cables are limited to 1M. It’s plenty long, but if you’re goping to do that, why not just put the drive inside the case – you’ll have to invalidate the warranty by opening the case to connect the cables up!

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