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Re: [PATCH] Loading windows in macbook

From: Yoshinori K. Okuji
Subject: Re: [PATCH] Loading windows in macbook
Date: Thu, 26 Jun 2008 03:48:51 +0200
User-agent: KMail/1.9.9

On Wednesday 25 June 2008 12:53:17 Bean wrote:
> On Wed, Jun 25, 2008 at 6:19 PM, Marco Gerards <address@hidden> wrote:
> > Bean <address@hidden> writes:
> >> On Wed, Jun 25, 2008 at 4:38 AM, Javier Martín <address@hidden> 
> >>> El mié, 25-06-2008 a las 04:11 +0800, Bean escribió:
> >>>> 2. Macbook will halt if we disable a20, so I add a new option
> >>>> --keep-a20 to keep the a20 gate open.
> >>>
> >>> Does any OS fail to boot if it has A20 enabled when it is jumped to?
> >>> AFAIK some BIOS even had an option to enable it at POST time, so I
> >>> think we should make this new option the default and have an option
> >>> called "--reset-a20" or something like that.
> >>
> >> I don't know of any os that would fail if a20 is enabled. Normally,
> >> they try to enable it as soon as possible as they need to access upper
> >> memory. So making it default is not a bad idea.
> >
> > It's disabled for legacy reasons.  Some old DOS applications expect
> > addresses to wrap around.  And thus a20 gate should be disabled.
> Right, but new version of dos will enable a20 as well, so application
> that depend on such feature would have serious compatibility issue.
> Anyway, the question is whether we should leave it on by default. A20
> is a common issue for buggy bios, I think we should leave it alone as
> much as possible.

No, no, no. Please don't forget the principle: a boot loader should pass 
control in the same environment as when directly booted, as much as possible. 
All sane PC BIOSes start with a20 disabled, so it must be disabled.


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