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I have an old r51 which I boot off USB. Apparently, if I have a Toshiba 2GB thumbdrive similar to this plugged in:

enter image description here

... or an old imation 1GB drive plugged in, it won't boot at all - it freezes in the BIOS loading screen until it's unplugged. I need to try it on another system but I'm wondering what could be causing it - since I suppose this is at a lower level than filesystem, and the drives work fine otherwise - even being readable if inserted after the system is booted from another source, with neither drive plugged in.

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I've noticed the same behaviour ... but a few seconds later in the boot process. Never thought much about it ... a glitch of some kind. Always works when you plug i tout ... the stick also works by itself. – Rook Jan 14 '10 at 5:05
I have seen that many times.. I have some memory of one time it happening with a USB printer! But that may have been a weird one-off.. i'm not sure if it was repeatable.. Normally these things repeat themselves i'm not sure why it didn't that time. I'm not sure if maybe i've seen it happen with a USB keyboard too on a tricky comp.. Be interesting if others find it has happened to them with USB devices other than disk drives. I wouldn't be suprised. And as with others so far. I don't know why it happens. – barlop Aug 8 '10 at 20:08

The BIOS will try to boot off of USB drives and CD drives depending on what is on the drive, BIOS settings and I assume that different manufacturers may have different notions as to how the BIOS behaves in the event of a non-bootable device.

If it can't find a bootloader on the device, it should go on to the next device. However, as in your case, the BIOS seems to hang on non-bootable devices that are attached to the computer. I've seen this happen with movie DVDs sometimes. The system can't find a bootloader on the drive and for some reason refuses to move on. (In the Windows 9.x era I was told that having a disc in the CD drive slows down the boot process. Ten years later, I understand what he was saying.)

Of course the drives will be readable after booting as long as there is real content on them. Again, the only reason they would not be read by the BIOS is the fact that there's no bootloader, which has nothing to do with how Windows or Mac OS X or Linux mount drives. The BIOS mounts the drive at some level to search for a bootloader. If the BIOS were capable of showing files on the drive it too would read your USB drive.

I think it depends on the BIOS, not the USB drive. You can make a USB bootable by installing Linux on it. Technically Windows will run off of a USB drive, but that may be illegal depending on how it is done.

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I disagree with that possibility since, that box boots off other USBs, and other USBs boot off that box. – Journeyman Geek Jan 14 '10 at 9:18
Like Said, it depends on what is on the USB drive. – Moshe Jan 14 '10 at 18:28

As Moshe said, the BIOS boots up from devices in the order specified. So if CD ROM is first & HD is second, & you have a music CD in the CD-ROM, some old PCs will get stuck trying to boot from the MUSIC CD.

The best bet is to make sure you set the prefered boot device as the first device BOIS should try booting from.

In your case since you want to boot from USB, only possibility is that you make sure no other USB device is connected other than the bootable USB Drive. Alos you can try & see which USB port does the BIOS read first so that you can attach your Bootable USB drive there & let other USB drives linger attached too. (Most probably the USB port at the backside have preference (faster) than the front side USB ports.)

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tried that. the drive boots off my main laptop. the laptop i'm usb booting boots off three other different drives. that's why i'm baffled – Journeyman Geek Jan 14 '10 at 9:19

Any chance your old BIOS only knows about old Master Boot Records (MBR) and chokes on modern GUID Partition Tables (GPT), and those flash drives use GPT instead of MBR for their partition maps?

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nope, basic normal, fat32/MBR drives. – Journeyman Geek Mar 27 '10 at 11:49

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