32- versus 64-bit fedora on an AMD 64 mobile athlon?

[John Summerfield]

Frank Cox wrote:
> On Mon, 31 Dec 2007 13:16:14 -0700
> Phil Meyer <pmeyer at themeyerfarm.com> wrote:
> 
>> If you are having students compile stuff, then you need to stick to the 
>> lowest common denominator (32bit) or else they cannot use those compiled 
>> programs elsewhere.
> 
> This is a bit of a niche issue, but it may be important with regard to certain
> applications.
> 
> You can use DOSEMU (http://www.dosemu.org) to run old (and new) DOS programs on
> Linux.  I wrote, support and maintain what has become a fair-sized suite of
> special-purpose programs for a particular industry.  For various reasons, the
> programs are written in PowerBASIC/DOS and run on Linux application servers
> under DOSEMU.
> 
> Linux/x86_64 runs DOS programs under DOSEMU approximately 13 times slower than
> they run on Linux/i386.  This is not as big of an issue as it may initially
> appear, because even 13 times slower on a 3+GHZ computer is faster than
> computers were running in back in the days when DOS was king of the hill. For
> an interesting description of the reason this happens, I highly recommend
> this article:
> http://thebs413.blogspot.com/2005/10/what-is-x86-64-long-mode-memory-model.html 
> 
> In short, running i386 Linux allows your CPU to use a “Virtual86” mode, while
> x86_64 Linux requires that the whole thing be emulated in software which
> obviously takes more horsepower and therefore runs more slowly

I have always assumed doesemu uses the 386's virtual-8086 mode, and 
that's not mentioned in Bryan J Smith's description above.





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Cheers
John

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