Re: Problems with to large of a kernel

H. Peter Anvin (
2 Dec 1998 06:33:21 GMT

Followup to: <>
By author: "Richard B. Johnson" <>
In newsgroup:
> 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.

Ah, yes; if the INT 15h memory copy function wasn't so bloody broken
it might actually be usable. *Sigh* It was of course too much IQ
required for anyone to have defined an A20 on/off BIOS function.


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