32/64 bit AMD question

[DebianTux23]

https://www.scientificlinux.org/

2005/10/19, Zach <uid000 at gmail.com>:
> It is a common misperception that "64-bits" means more/better
> performance than "32-bits".  This is not (necessarily) the case.  For
> those who don't remember, when we transitioned from the 16-bit 8086
> and 286 to the 32 bit 386 in the 80's, the new 32 bit processor wasn't
> faster, at least not because of "being 32 bits".  386's were faster
> than 286s because of higher clock speeds, architecture optimizations,
> and things like this.  However a 32 bit x86 cpu could let you do
> things that you couldn't do with the 286, assuming software developers
> took advantage.  These included addressing more memory than the 286's
> 1mb limit, virtualized memory mapping (each process thinks it's the
> only one running), multitasking, as opposed to task swapping which the
> 286 was capable of, and other things.
>
> The same thing applies to the transition to 64 bit x86.  The main
> difference here is that systems now can address more than 4gb of ram.
> If your application benefits from more than 4gb ram, then you might
> see a performance benefit there.
>
> The Athlon 64 is faster than Athlon XPs due to a completely new
> architecture, not because of being "64 bits".   It features things
> like the memory controller being right on the cpu die, as opposed to a
> chip on the motherboard, and things of this nature.
>
> As mentioned perviously, 754 pin socket vs the 939 pin socket doesn't
> cripple the "64-bitness" in any way.  The difference is the cpu can
> address two banks of memory at once vs just one.  This is only going
> to benefit applications and games that are starved for memory
> bandwidth.
>
> Hope this helps clear things up.
>
> On 10/19/05, Lewis Futrell <silicon.vampire at gmail.com> wrote:
> >
> >
> >
> >
> >
> >  Maybe put another way, what is the performance difference in 64 bit mode
> > compared to 32 bit, of the 754 pin and the 939 pin AMD Athlon64's for the
> > same clock speed?
> >
> >
> >
> >  The funny thing is, it is exactly the memory interface that is different
> > between the two.  The 754 socket only does single channel memory (64 bit
> > path) whereas the 939 CPU's are dual channel (128 bit path).  The 64 bit
> > part of the processor is the same.  The performance difference will be the
> > memory bandwith.
> >
> >
> >
> > Thanks Lewis, does that mean that in 32bit mode the chip only does 32bit
> > memory accesses but in 64 bit mode the 754pin chip does 64 bit and 939 pin
> > chip does 128bit (memory access not calculations)?
> >
> >  If true, then 64 bit mode should be faster than 32bit in both chips, but
> > the 939 will be faster (by the memory access time) then the 754. Do I have
> > this understanding correct or am I still missing something?
> >
> >  Regards Russell.
> >
> >
> >
> >
> >
> > That is correct.  However, in most tests that I've seen on the review sites,
> > the performance increase between 32 and 64 bit mode varies upon the
> > application one is doing.  Sometimes 32 bit mode is just as fast, if not
> > slightly faster than 64 bit, and vice-versa.  The biggest issue that you may
> > want to look at is to see if there are 64 bit versions of the
> > programs/applications that you want to run.  For example, there is not a 64
> > bit version of Flash that I'm aware of (one can do a chroot environment to
> > run 32 bit applications in 64 bit Linux, but that is a little over my head).
> >  Also, some drivers do not have a 64 bit version of them, but this is
> > thankfully being worked on and the likelihood of having a device that won't
> > work on the 64 bit version of Linux is becoming less and less of an issue.
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> >
> >
> >
>
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