linux-kernel - Re: how to tell linux (on x86) to ignore 1M or memory

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Message-ID: <467B29DA.9040309@zytor.com>
Date:	Thu, 21 Jun 2007 18:46:02 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Rene Herman <rene.herman@...il.com>
CC:	Bart Trojanowski <bart@...ie.net>, linux-kernel@...r.kernel.org
Subject: Re: how to tell linux (on x86) to ignore 1M or memory

Rene Herman wrote:
> On 04/19/2007 04:18 PM, Bart Trojanowski wrote:
> 
>> I need to preserve some state from the bios before entering protected
>> mode.  For now I want to copy it into some ram accessible by
>> real-mode, say the last megabyte visible in real-mode.
>>
>> What's the easiest way to have linux ignore the megabyte starting at 15M?
> 
> Note that real-mode can only access the first megabyte (*) and not the
> first 16. 16MB is the 16-bit protected mode (286) limit.
> 

No, 16-bit protected mode (on 386+) is not limited to 16 MB.

The main reason there is a 16 MB limit in some current systems is that
ISA, and the ISA DMA controller only had 24 address lines.

	-hpa
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