Re: Problems with to large of a kernel

Richard B. Johnson (
Tue, 1 Dec 1998 14:50:57 -0500 (EST)

On Tue, 1 Dec 1998, Alan Cox wrote:

> > Yes, I've done this. However, when trying to use that kernel on a floppy
> > disk for installation (we build nearly 50 servers a month for our business),
> > you cannot boot off of a floppy using that kind of kernel image.
> I boot bzImages off floppies all day every day on my PS/2 model 77, since
> Lilo seems to dislike the machine. I've had no problems. Could this be
> some kind of BIOS/A20 problem ?
> Alan

BzImage kernels use the BIOS INT 0x15 'memory copy' function to put
the kernel at its final resting place of offset 1 megabyte which
is unreachable in the 16-bit segment:offset world. Since this function
is enabled and tested by the BIOS as part of the memory check, it is
not too likely that it is broken. There was a problem with stuck
A-20 bits in early '386 machines that used the keyboard controller
to enable it. Basically, you had to wait a few microseconds to have
it take affect, since the keyboard controller is really its own CPU
with embeded software that takes time to do its thing. A BIOS would
certainly "know" the time to wait, so it would be embeded in the
INT 0x15 code. The problem occurs when a user program tries to enable
the bit and expects an instant response.

Dick Johnson
Penguin : Linux version 2.1.128 on an i686 machine (400.59 BogoMips).
Warning : It's hard to remain at the trailing edge of technology.

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