On Tue, 24 Feb 1998, Stefan Reinauer wrote:
> > A standard BIOS doesn't know about the file system, all it does is
> > load the first sector on the disk. The rest is up to the boot loader
> > of the operating system.
> Wrong. Current BIOSs have a simple MSDOS system in their int-Code. MSDOS
> even doesn't have it's own filesystem code afaik..
According to all the BIOS code I have read, BIOSs do not have any
filesystem code. As outlined before, all they have is sector,
cylinder and head code.
> > This is generally based on a trial and error detection procedure
> > (set biggest possible size, then find out how many address bits
> > really work), rather than presence detect bits.
> Again, modern PC Chipsets allow reading the exact RAM configuration out of
> their registers
Yes, in a proprietary way.
I would like to take this opportunity now to stop and as "Why?"
I'm sure it's been brought up, but I don't see the need to rein-
vent the wheel when it comes to BIOSs. First off, don't all PCs
come with BIOSs? Second, writing a generic BIOS that will encom-
pass all the new motherboards, IMO, will be a wasted effort.
Aren't the majority of PC chipsets proprietary on how they are
initialized for caching, memory configurations, et al? Personal-
ly, I see this project as a waste of programming power. As it
was said earlier, the only forseeable benefit is to LILO (ini-
tially). I don't see much support after that either, unfortu-
The idea of replicating the BIOS programming interface is not a
worthy effort either, IMO. Everyone agrees that it is old, ante-
quated, and kludged. The idea of rewriting all the BIOS routines
anew without the legacy baggage is a good idea, but I don't think
that you should "hide" the fact that you are doing it. I think,
if you are going to rewrite the BIOS routines correctly, a unused
interrupt vector should be chosen, and a completely new set of
routines should be written. Or perhaps, simply writing a com-
plete set of routines to be loaded overtop of the BIOS, so that
any programming wanting the GNU BIOS routines would simply in-
clude the object file, and call a initialization routine or two
(provided of course they are taking complete control of the sys-
tem). Those are my ideas for the current project.
As an offshoot from this project, I have an idea that I can per-
sonally use (or, more specifically, that I wanted to use). Ac-
cording to the documentation I have, memory locations from C8000h
to E0000h are checked at 2k intervals for the sequence "0xAA55"
If it is found, the next byte is a "length indicator representing
the number of 512-byte blocks in the ROM." Following that is a
far code entry point. The entire ROM also has to be checksummed
modulo hex 100 and come up to 0. I think this interface can be
used to produce a LILO of sorts that can replace the initial boot
loader. A command line interface can be supplied, as well as
some code that would investigate the current hard drives, and
their partition tables. This could produce a BIOS that is simi-
lar to many older "minicomputer" style BIOSs. This interface is
checked after all of the initialization sequence occured, and be-
fore any bootstrapping. That way, a more modern BIOS can be
written without the worry of compatibility between all sorts of
different hardware. This has other practical values as well.
Since every single PC in existance has a ISA bus, but not all PCs
have the same BIOS chip (not even the same number of chips, or
the same number of pins), this allows for better distribution.
It allows faster development time, since you can easily remove a
card to boot the machine to a useable state again. (as opposed to
gerryrigging some sort of external platform with a mechanical
switch.) Also, hardware illiterites are more comfortable in-
stalling an ISA card, as opposed to removing chips off of the
As for my experience, I have been programming in Assembly lan-
guage for 7 years now, concentrating on low level VGA program-
ming, rudamentary OS code, as well as custom cards. I have two
BIOS listings, one is a 386+ BIOS reverse engineered (obtained
freely from x2ftp.oulu.fi I believe). The other is in the back
of the IBM Technical Reference Personal Computer AT, 1985. This
code is original IBM BIOS code for the 286. (Did you know that
they tested each register, conditional jumps and the BOUND in-
Whichever way the project desides to go, I wouldn't mind helping
out. I have experience in this area, and I would like to prac-
tice my skills in something, that might, quite possibly, do some-
thing, for someone, somewhere. ;)
Vic/Linux and Pet/Linux: RPMs coming soon.