In case any one else comes here with a genuine interest in write-protecting boot media against possible firmware-based malware, reads the first few posts about a USB stick and skips to the end to find mention of replacing BIOS USB drivers and even open-sourced BIOS replacement project CoreBoot, please don't waste your time (as I did) reading the rest this thread trying to discover how they might relate, because, for all practical purposes, they don't. The most interesting information (in my opinion) within was actually when the thread was temporarily derailed into a somewhat off-topic discussion on the efficacy (and apparent lack thereof) of SD card write-protect switches. You can find most of that on page 2, I believe. But from the point that Popov redirects the discussion into troubleshooting his own 4GB USB flash stick write-protected boot issues this summary should do:
1) By means of various (and later exhaustive) imaging tests, it's established pretty early on that Popov's USB stick is either a flawed model or is individually defective in that his write-protect switch also fundamentally changes the read mode of the device to (apparently imperfectly) emulate a floppy. Time and again regardless of hardware or software platform Popov doggedly returns test results to indicate that his USB stick a ) successfully boots with the switch set to off but b ) fails to boot with the switch set to on.
2) Possibly motivated by some combination of sadomasochism and/or scholarly interest, Wonko and MedEvil continue to encourage Popov in his misguided efforts by suggesting test after redundant imaging test until they finally devolve into what appears to be the the tail-end of an argument (probably begun elsewhere) between themselves on the merits of the plop bootloader USB driver. While Wonko is apparently for it and MedEvil against, neither offers any especially supportive evidence to back their positions.
3) After plainly and repeatedly demonstrating a fundamental lack of subject-matter understanding, in the course of testing Popov finally mistakenly destroys his hard-disk partition table and expresses very understandable concerns over valuable personal data loss. Nevertheless undaunted and evidently equipped with much more free time than purchasing power (or common sense), when we last hear from Popov he is considering replacing his laptop's BIOS firmware with the extremely experimental and almost certainly unsupported open-source CoreBoot project.
4) Considering Popov's boundless (and witless) determination up to that point, we can assume that we haven't heard from Popov for three weeks now because he actually did attempt to replace his manufacturer's BIOS with CoreBoot, failed miserably in said attempt, and can therefore no longer boot at all let-alone access the internet to apprise us of the situation regardless of his 4GB USB flash drive's write-protect switch setting.
Wow.
Still, just in case I'm not too late and Popov still is out there somewhere, I have this advice to offer him:
Troubleshooting should result in an economical solution, not more problems. Remember Occam's razor and always start your troubleshooting with evaluating and/or replacing those components that are most obviously related to your issue and that are cheapest/easiest to replace/evaluate.
Popov, don't flash over your BIOS with CoreBoot to solve a problem with your USB stick. Instead, consider booting with the switch set to "off," or even, just maybe, try another USB stick. Seriously, I'm astounded that throughout 5 pages of forum posts and test after redundant test, no one once suggested this. At some point, Popov, you've just gotta cut your losses; know when to fold 'em, as it were.
Happy Hunting!
Edited by mikeserv, 05 May 2013 - 02:01 AM.
) PLoP is the only one that has it's own USB stack, Medevil is 100% correct on this.
Good mooorning, Mr. de La Palice! 
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