[ILUG] [TOTD] flash bios in linux

[Ronan Cunniffe]

On Fri, 13 Aug 2004, Timothy Murphy wrote:

> Are you sure this isn't an urban myth?

Yes.

In the bad old days when 64KB cost a lot of money and 4.77MHz was fast,
the BIOS EPROM was mapped into the last 64KB of the lower 1MB, and BIOS
calls were executed from the EPROM directly.

EPROMs are *slow*.

Shortly thereafter, manufacturers got a clue, and copied the EPROM code
into real RAM at boot-time and the BIOS calls were executed from there.
 (ISTR 250+ns for EPROM vs. 120ns for 30pin 286 era DRAM??)

In other words, for a very long time now, the EPROM (flash these days) is
powered-but-idle except during boot and the bridge chip driving
the socket won't notice anything so long as you can avoid nuking it with
static - and good luck getting the board to boot if you do *that*.

> I've often read of it,
> but never met anyone who had tried it,
> let alone succeeded.

I haven't done it with a PC.
I did it accidentally in college with a lab-built board.
Nobody noticed until my team-mate tried to test the application I had
just physically removed and stuck in the UV-eraser....

Ronan