Re: [9fans] non-BIOS boot

[Ronald G Minnich <rminnich@lanl.gov>]

On Thu, 30 May 2002, Don wrote:

> If you dont use the BIOS wouldn't you have to access
> the disk via i/o ports? If so, you would have to adhere to
> the SCSI/ATA standard rather than a more conformed interface
> via int13?

Great question. I used to think this too.

Turns out PC hardware is designed for two things: full-capability OSes and
really STUPID STUPID BIOSes. So, for example, IDE hardware runs with all
kinds of fancy DMA, and also runs in trivial polled-IO modes so that
software written ca. 1982 will work correctly. It's really amazing to see
the contortions PC hardware goes through to conform to an Intel reference
design from 1978 or so (not kidding, I have some of those old books
somewhere).

It turns out that the INT13 is no more conforming than the silly hardware.

What we do in LinuxBIOS for IDE support is run dead-stupid simple
polled-IO drivers to load the kernel. These were contributed by someone
from another project.

 > If you did have to adhere to the different standards
> wouldnt that mean implementing the drivers in the MBR/PBS?

Yes, you are right here, but this has turned out to be not a big deal (so
far).

ron