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Re: "Trivial Question" - 32bit vs. 64bit vs. 32/64bit

Thanks for the info.

I need to investigate which drivers I will need (they're all going to change 
with the new motherboard!) to see whether it makes sense for me to migrate to 
a 64bit kernel.

It really sounds like Debian isn't quite ready/equipped for the whole 
simultaneous multiarch situation (itself just the general case of the biarch 
setup, I would think).  Perpaps I'll try SuSE, but I'm not really interested 
in learning a new dist.  I like the way Debian's structured and I'm pretty 
familiar with it.

Once again, thanks for your help.  Now to draft what I've learned into a FAQ 


On Thursday 27 May 2004 17:11, you wrote:
> Chris,
> It doesn't seem like anyone has really answered a couple of your questions.
> I'm doing this back channel cause I don't want to get in the middle of the
> fray, there is considerable disagreement over the multi versus bi
> architecture stuff.  Personally I don't care as long as x86 binaries run on
> my 64bit system.
> > I have read/skimmed the AMD64 Debian HOWTO, but still don't 
> > know the answer to 
> > the general question: Do I want a "pure" 64 bit system, or 
> > not?  It seems 
> > like there's a 32 bit "compatibility" mode (that had a root 
> > exploit), but I 
> > don't know how that works (generally speaking).  Do I have to 
> > keep around a 
> > whole separate /lib32 directory (as opposed to a /lib64 one)? 
> >  How would I go 
> > about running GL games, like Quake, Critical Mass and Return 
> > to Castle 
> > Wolfenstein?  Does ALSA work in 64 bits?  Do nVidia's video drivers?
> The way this works is that the chip has 32 and 64 bit modes. In 64 bit mode
> you have nearly double the number of registers and they're typically twice
> as wide. In 64bit mode the address space is a flat 64-bit unsegmented
> virtual address space.
> If you want to use the 64 bit mode the operating system must be running in
> 64bit mode.  With the OS running in 64bit mode applications can run in
> either 32 or 64 bit mode. Applications running in 64-bit mode have the
> additional registers and they're 64 bits wide.  Applications running in 32
> bit mode only see the registers the would on a 32 bit system and they're 32
> bits wide.  The 32 bit process also sees the segmented address space it
> normally would.
> If an application is running in 32 bit mode it's libraries must also be
> running in 32 bit mode. So on a system that supports both style of
> applications you need duplicate libraries.
> As far as the kernel is concerned, if it runs in 64 bit mode all of it runs
> that way. The implication of that is that if you're running a 64 bit kernel
> you need 64 bit versions of any driver you want to use.
> The big controversy around this dual environment is that the LSB tells you
> where to put the libraries and applications. I haven't read it myself but
> think that it specifies a /lib and /lib64 heirachy with /lib being reserved
> for 32 bits.  One of the problems though is that on 32-bit systems /lib
> contains 32-bit libraries and on 64-bit systems like Alpha and IA64 /lib
> contains 64-bit libraries.  The Debian folks don't like the idea of separate
> 32 and 64 bit libraries. To further complicate the picture at least Redhat
> ships and x86_64 distro with /lib and /lib64.  It's a mess.....
> > 
> > Applications aside, I thought the Opteron could run either 
> > 32bit stuff or 
> > 64bit stuff natively.  If this is so, then why does there 
> > need to be a 
> > software compatibility mode?
> > 
> > Can someone please help me out with some of the basics of 
> > migrating to 64bits?  
> > I promise I'll try to generate some sort of document to help 
> > out others 
> > (suitable for addition to the HOWTO).
> Frankly I'm waiting for the debian folks and the community to work through
> this.  All my ia64 and x86 boxes run debian.  My Athlon and Opteron boxes
> run Redhat or SUSE.  It's great to have a 64bit system and beable to just
> run x86 binaries. 
> 	ray

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