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Date: Thu, 06 Nov 1997 14:12:14 -0600
To: Terry Lambert <tlambert@primenet.com>, mike@smith.net.au (Mike Smith)
From: Tony Overfield <tony@dell.com>
Subject: Re: >64MB
Cc: hackers@FreeBSD.ORG
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At 06:47 PM 11/6/97 +0000, Terry Lambert wrote:
>> How do you copy the kernel into memory > 1M in real mode?  
>
>There are several ways to do this.  The main one uses a call that drops
>into protected mode, changes a 64k mapping at the top of the 1M
>you can get at, and goes back to protected mode.
>
>You can see a nice example of this in your config.sys on most DOS
>machines, where you probably load an EMS, XMS, or DPMI driver so
>DOS (and more likely, Windows 3.x) can use memory above 1M.
>

I can't tell, but I think you're talking about one of these:

1.  ... switching to protected mode, setting larger segment limits
    and then switching back to real mode.

    It's very unlikely that you have anything in your config.sys 
    that uses this trick.  There's no benefit to using it, and 
    there are serious compatibility problems with it.

2.  ... the real mode trick of using FFFF:xxxx addressing.

    This lets you address up to 64K-16 bytes of memory above 1M in 
    real mode.  Protected mode is not needed to enable or use this 
    trick.  It is completely inadequate for loading a kernel.  In 
    DOS, this is called the HMA "high memory area".  It is used 
    when use have DOS=HIGH in your config.sys, as one example. 

3.  Something else.  
    If so, please state it more clearly.

-
Tony