Itanium2/Xeon64/Opteron 
Author Message
 Itanium2/Xeon64/Opteron

We would like to purchase a shared memory machine with several processors
with the CPUs mentioned above. Since most of our applications are in fortran
we will greatly apprciate any opinions or advise on this matter.
Also is it true that the Opteron is actually a 32bit CPU with memory
addresing capability to 48bit?
Many thanks for you kind help. Best, MH.


Fri, 21 Jul 2006 00:36:08 GMT  
 Itanium2/Xeon64/Opteron
(I hope 2 copies of this don't show up.)

Quote:

> Also is it true that the Opteron is actually a 32bit CPU with memory
> addresing capability to 48bit?

Mostly statements like that are meaningless.  I don't recall specifics
of the Opteron architecture, so I can't comment on that part, but I
know to be dubious whenever anyone uses the term xx-bit CPU as though
it means something.

The description of CPUs as xx bits has more to do with marketing than
with any actual technical features of the CPU.  The definition varies
at the whim of marketing departments.  I still have manuals from
Intel documenting the 8088 as an 8-bit CPU.  Later manuals documented
the same chip as 16 bits.  The chip didn't change - just the definitions.

To make a question like that meangful, you'd first have to define
what you mean by a 32-bit CPU ("actually" or otherwise).  There are
lots of possibilities.  Though there is no universally established
definition of xx-bit CPU, the most common usage today is that xx is
the address width.  By that definition, it would be a contradiction
to say that a CPU was 32-bits with 48-bit addressing.

There may well be some other definition that makes the statement
sensible.

But unless you are in the marketing business, you'd be better off
finding out what is actually meant.  Avoid ill-defined terms like
xx-bit CPU completely.

--
Richard Maine
email: my last name at domain
domain: sumertriangle dot net



Fri, 21 Jul 2006 01:35:47 GMT  
 Itanium2/Xeon64/Opteron

Quote:

>Also is it true that the Opteron is actually a 32bit CPU with memory
>addresing capability to 48bit?

The Opteron is a 64-bit cpu in the usual meaning of the label: It has
general purpose 64-bit integer registers, and addresses a lot of both
real and virtual memory.  Like all other 64-bit cpus, it doesn't have
all 64 bits of virtual address, but it has enough that you aren't
going to run out.

There's a good comp.arch posting by John Mashey on 64-bit cpus that I
could dig up, if you like.

-- greg



Fri, 21 Jul 2006 04:32:27 GMT  
 Itanium2/Xeon64/Opteron

(snip regarding CPU bit width)

Quote:
> To make a question like that meangful, you'd first have to define
> what you mean by a 32-bit CPU ("actually" or otherwise).  There are
> lots of possibilities.  Though there is no universally established
> definition of xx-bit CPU, the most common usage today is that xx is
> the address width.  By that definition, it would be a contradiction
> to say that a CPU was 32-bits with 48-bit addressing.

How about the geometric mean of the address bus width, data but
width, register width and ALU width?

-- glen



Fri, 21 Jul 2006 07:37:34 GMT  
 Itanium2/Xeon64/Opteron

Quote:
> Like all other 64-bit cpus, it doesn't have all 64 bits of virtual address,
> but it has enough that you aren't going to run out.

I thought they specified as future extension a page-table format that
would allow to use all 64 virtual address bits. However, as long as the
implementation restricts the physical address bits and not very many people
have 64 bits worth of even virtual memory available, I'd consider the
discussion academic.

All 64 bits are checked by the hardware, though, so you can't squeeze
through with 68000- or S/370-like kludges.

        Jan



Fri, 21 Jul 2006 17:26:07 GMT  
 Itanium2/Xeon64/Opteron



Quote:
> We would like to purchase a shared memory machine with several processors
> with the CPUs mentioned above. Since most of our applications are in
Fortran
> we will greatly apprciate any opinions or advise on this matter.
> Also is it true that the Opteron is actually a 32bit CPU with memory
> addresing capability to 48bit?
> Many thanks for you kind help. Best, MH.

in the Opteron:
bus adress is 48bit (?)
data bus width is 128bit
-and in 64 mode : all integer registry have be extande to 64 bits,
Floating point still 80bits
SSE2 still have 64 or 32 bit floating point support
SSE1 still have 32 or 16 bit floating point support
MMX still have 16 or 8 bit integer support

and have 3 floating point core, 3(?) ALU core

(and if I think Athlon have 40bit virtual memory adress support....)

But unlike other 64 processor, the Opteron can work in 16bits, 32bits or 64
bits mode....

but AMD have complet desciption on are site....

  Djip



Tue, 01 Aug 2006 06:30:53 GMT  
 Itanium2/Xeon64/Opteron


Quote:



> > We would like to purchase a shared memory machine with several
processors
> > with the CPUs mentioned above. Since most of our applications are in
> Fortran
> > we will greatly apprciate any opinions or advise on this matter.
> > Also is it true that the Opteron is actually a 32bit CPU with memory
> > addresing capability to 48bit?
> > Many thanks for you kind help. Best, MH.

> in the Opteron:
> bus adress is 48bit (?)

48 virtual, 40 physical
Quote:
> data bus width is 128bit

only in the same sense as other competing processors
Quote:
> -and in 64 mode : all integer registry have be extande to 64 bits,
> Floating point still 80bits

but Microsoft "64-bit" OS forbids use of those registers
Quote:
> SSE2 still have 64 or 32 bit floating point support
> SSE1 still have 32 or 16 bit floating point support

nothing for Fortran in the 16 bits there
Quote:
> MMX still have 16 or 8 bit integer support

nothing useful for Fortran there
Quote:

> and have 3 floating point core, 3(?) ALU core

2 64-bit FPU's vs 1 parallel (4x32 or 2x64) for competitors
Quote:

> (and if I think Athlon have 40bit virtual memory adress support....)

since when? probably has 36-bit PAE, like P-III et al, but we can forget
that now.  Never was useful for Fortran support.
plenty of more enlightening guesses, for those who care to look, may be
found by Googling.


Tue, 01 Aug 2006 11:51:28 GMT  
 
 [ 7 post ] 

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