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I don't get it. Why is it so complicated to create a bootable usb from a disc image?

Disc images have boot sectors, so why can't you just write the raw LBA values from an image directly to a USB and be done?

I haven't see any tool for Windows that lets me do this.

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6 Answers 6

Ok I see the problem. The LBA sizes are different on USB and CD-ROM drives. 512 vs 2048.

So a boot sector designed for a CD won't run on a USB drive.

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It's not the block size, it's that the boot format is completely different. (El Torito) You can absolutely write a byte-for-byte copy of an ISO-9660 filesystem to a USB disk, but no normal BIOS will recognize it as such. There's no fundamental reason why one couldn't, especially if it implemented an emulation layer to make the USB disk look like a CD. –  Captain Segfault Oct 17 '09 at 1:12

Try Unetbootin, it works for Linux distros. Also surf on over to the hak5 website, they had a couple of episodes dealing with what they call the USB mutlipass for putting multiple isos on a usb drive.

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This one installs a linux boot sector...the ISO already contains one! I just want the exact contents of a bootable ISO... –  Pyrolistical Oct 16 '09 at 0:31
@Pyrolistical: Then you clearly don't understand the boot process, nor what the Unetbootin tool does - way oversimplified, it essentially creates a boot record on the flash drive and dumps the contents of the ISO onto the flash drive. There are also other potential issues beyond just the sector size, the BIOS can interpret (then emulate) a flash drive as many different types of media. Even CDs back in the day had a number of methods. It is WAAAAAAAAY more complex (and far beyond the scope of this site) than simply extracting the boot records and raw files. –  Goyuix Oct 16 '09 at 19:23
This worked for me to burn a bootable .img image. Just select the .img file, but make sure you choose ISO, not Floppy on the drop down. –  Derrick Aug 31 '12 at 19:17

It is possible but not straightforward: http://www.boot-land.net/forums/index.php?showtopic=6436

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FlashBoot, although not free, is a great tool to make USB drives bootable. It supports converting a CD image to the USB drive.

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This does not appear to allow burning of image files –  Derrick Aug 31 '12 at 17:11

Ah, I would definitely recommend UltraISO Its asks you to pay, but is free to try for as long as you like with no features missing, and no annoy ware (ie. pop-ups every few minutes), It is really easy to use and will write bootable iso's to thumb drives and cd/dvd's (Ive used it for win7 and ubuntu), it will also give you full control over the iso to selectively copy items over.

* As of 5/1/2012 unregistered software is crippled with 300mb limit

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Pyrolistical, your own answer is correct - bootsectors for different types of drives (CD, HD, floppy, etc.) are different. That's not to say that you can't do a similar thing to ISO images with other types of drives. WinImage should be able to do it, though I haven't actually tried with a USB drive. (Google reports it as an "attack site" for some reason - I'm not sure why.)

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It's listed as an attack site because it installs various Trojans. Assuming it was originally a real site, Russian hackers (from the domains involved) would seem to have taken it over. –  CarlF Oct 16 '09 at 5:12

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