I generally agree with you, but...
Linus Torvalds <[email protected]> writes:
> And it not at all uncommon to have a flash that simply cannot be upgraded
> without opening the box. Even a lot of PC's have that: a lot (most?) PC's
> have a flash that has a separate _hardware_ pin that says that it is
> (possibly just partially) read-only. So in order to upgrade it, you'd
> literally need to open the case up, set a jumper, and _then_ run the
> program to reflash it.
I think this is history. Yes, late 486s and Pentiums (60 and 66?)
had a jumper protecting the flash. It's not true since ca. "Pentium 75+"
days - while many boards use "bootblock" chips, it's (almost?) always
unprotected (at most it just requires setting some GPIO pin(s)). The
rest of flash obviously has to be R/W to support the ESCD etc.
I think there are systems with 2 copies of the whole BIOS, and the
user selects the copy with a jumper (probably connected directly to
the most significant address line of the flash IC) - the second
copy might theoretically use a R/O bootblock but I've never checked it.
Most VGAs, disks, PCI cards etc. have flash chips with no protection
either, and I have to say I felt much better when they used (EP)ROMs.
I think almost all hardware manufacturers use a blank flash chips,
programming them "in system" with things like JTAG.
--
Krzysztof Halasa
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