Re: ISA Memory hole at 15-16 MB

From: Erik Mouw (
Date: Thu Aug 03 2000 - 10:54:53 EST

On Thu, 3 Aug 2000 17:34:19 +0530 , Abhishek Khaitan wrote:
> While I was going through the Linux Device Drivers book by Allessandro
> Rubini, I came to know that at the time of 286 computers, ISA memory was
> mapped between 15 and 16MB for RAM. Since at that time nobody had more than
> 1-2 MB of RAM, people had no problems accessing the ISA memory.

More or less correct. Some high-end (well, at that time) video cards could
map their video memory linear at 15-16M.

> But now, as everybody has around 64MB RAM, so when we access that memory
> between 15 and 16MB (the ISA memory hole), are we referring to physical RAM
> or to ISA card's memory?

Physical RAM, although some PCs still allow you to create a memory hole
from 15-16M to accomodate the use of those old ISA video cards.

> Where can I get more details on this?

Your computer's BIOS manual.


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