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I don't have an active problem with this but I am curious.
Over time, my repair work has led me to experience many instances (repeatable and reliable ones) where a computer (desktop or laptop; every situation is unique but is consistent in itself) has problems during the POST/boot phase of startup.
An example: One computer hangs during boot (I forget exactly where, but it's after POST) when I have an external USB storage media in it. This can be a hard drive or a USB drive. It's not EVERY USB HDD or Flash stick, but it is a significant number. So much so that when I boot, I try to make sure it doesn't have these devices plugged in. I can't remember if it matters WHICH USB port(s) is used, but I typically use the front ones.
Another example is a laptop that I worked on, which hung after POST when an Ubuntu LiveUSB was plugged in, unless I used a specific port, which was almost completely destroyed inside.
A third example is another desktop machine which, when booting while a USB hard drive is plugged in, hangs during boot at the point where you see text on the screen. During the pre-OS boot phase. If I unplug the hard drive, the boot immediately resumes as if there were no problem.
Why would external devices (some bootable, some non-bootable) cause this kind of boot issue? It's wide-spread, and non-uniform, and I'm curious what happens at a machine level.
Is it not a motherboard standard to be able to look past undetected devices like these? I've seen motherboards before report that it could not identify devices (hard drives, in particular) that were plugged in by SATA or IDE. – jwarner112 – 2013-10-14T14:59:48.143
Yes, a motherbioard (well, BIOS, UEFI, ...) should be able to look past that. Should being a keyword. Many simply fail when they get something unexpected (e.g. a GPT formatted drive on an old BIOS. Where it should just skip over it rather than crash). – Hennes – 2013-10-14T15:44:27.070