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Re: Fw: 16-bit bootloader support?

From: Bogdan
Subject: Re: Fw: 16-bit bootloader support?
Date: Thu, 8 Oct 2009 16:45:50 -0700 (PDT)

The difference is basically that you have no paging, the linear address is the 
same as the physical address, no virtual 8086 mode, no way of going back to 
real mode, the segment address inside the descriptor table is 24 bits wide and 
the limit is 16 bits wide.

In response to Seth - there are still business and apparently research machines 
out there that still use the 80286. It's arguable whether one would actually 
need to be able to boot several OSes on such machines but I am an example of 
someone who is personally interested in this. If I write support for this can 
it be merged into GRUB (and the spec)?


Bogdan wrote:
> I'm sorry for the top-down mail but Yahoo! Mail is gay. No, I don't mean 
> virtual 8086 mode, I mean the 16-bit protected mode - which is 16-bit and not 
> 32-bit. Protected mode was introduced on the Intel 80286 which was still a 
> 16-bit CPU. Protected mode was later extended for 32-bit allowing of course 
> for backward compatibility. Windows 3.1 is a good example of an OS capable of 
> handling 16-bit pmode.
What is the difference between 16-bit and 32-bit protected mode? Is
16-bit protected mode like 32-bit protected mode, not paged mode but
with upper 16-bits ignored?
What are the benefits of supporting it?
> It's not legacy code I'm talking about.
> Cheers,
> Bogdan
> Bogdan wrote:
>> Most probably the developers of GRUB will say that this is useless but
>> did anyone think of adding 16-bit protected mode support to the
>> Multiboot specification and to GRUB?
> Which mode do you mean?
> protected mode=32-bit mode
> You may mean vm8086 mode but it's meant only for compatibility purposes.
> As such it's an OS responsibility to set it up when executing legacy code
>> Cheers,
>> Bogdan
> _______________________________________________
> Grub-devel mailing list
> address@hidden

Vladimir 'phcoder' Serbinenko
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