Anyone plz mension the advantages of 64-bit processor in numerical computations!!??

precison is higher and results are more accurate

does it improve the computational speed??

64 bit processors will give better performance on long float operations (FORTRAN double precision)

they also provide 64 bit pointers for memory allocation with the possibility to adress (2**63 -1) bytes of RAM memory as opposed to 32 bit architectures' (2**31-) bytes.... the well known 2Gig limit found on most PCS....

Rubbish on two counts:

1) Stored precision is the same regardless of the chip. A double will be 8 bytes on 32-bit and 64-bit systems.

2) Arithmetic is typically carried out using 80-bit registers and the results are truncated on copying into regular memory.

The real advantage with 64-bit processors is that they can address more memory and can read/write bigger files. Most non-trivial CFD requires more memory than a 32-bit processor can address.

For some codes, if you are going to build models larger than 5 million cells you must use a 64 bit machine. Tom

Well said.

I can add one point to this;

Standard main-stream 64 bit platforms have the same memory restrictions as 32 bit platforms.

A 64bit platform can access memory up to 64bits. That's why they call it a 64bit platform. A 32bit platform can only access 32bits. They most certainly do not have same memory restrictions.

> A 64bit platform can access memory up to 64bits. That's why they call it a
: 64bit platform. A 32bit platform can only access 32bits. They most
: certainly do not have same memory restrictions.

They do if the operating system code and libraries are only 32 bits.

I agree with you Andy but Ford Prefect didn't say anything about operating systems - just "mainstream 64bit platforms". Every mainstream 64bit platform I know of (IBM-AIX, Mips/Irix, alpha/Ultrix, Pa-risc/HP-UX, sparc/Solaris...) have had 64bit hardware and operating systems for years. Opteron/linux64 has been around for at least 2 years, maybe more. Even Microsoft has had Win64 out now for some time so I don't know what else a "mainstream" platform could be? His remarks didn't make any sense.

does the version of the compiler affects the performance. and if so (as i think) plz suggest one!!

If you have UNIX box witha vendor-supplied compiler (e.g. Sun/SGI/Alpha/IBM/HP), then no - they all support 64-bit building. However, FORTRAN compilers for Linux and Windows are generally 3rd-party ones (ignoring g77 of course) and not all versions can build 64-bit applications. Check the box before you buy.

For Itanium-2 processors Intel provides C/C++ and Fortran compilers fully supported for 64-bits applications

For Opteron processors you'll need to buy the Portland Group compiler (I guess, it's the more well known).

There are Sun stations with Opteron processors where you can use the Sun Development Studio. It's free and also support 64 bit's applications.

TG, to clarify:

First: I do not define "(IBM-AIX, Mips/Irix, alpha/Ultrix, Pa-risc/HP-UX, sparc/Solaris...)" as mainstream. Mainstream CFD computer perhaps, but not just mainstream.

Second: Buy a mainstream motherboard, say a sock. 939 from MSI or ASUS. Use a 64 bit processor, either amd64 or opteron. Then try filling the memory slots with more than 4 gigs of ram (the same ammount available to standard 32 bit platforms). You will probably end up with a cpu that can address more memory but a motherboard that can't fill it's needs...

/F

Intel do not "provide" compilers. They sell them.

It's true for Windows platforms but for Linux platforms you can get a free non-comercial license.

You can go to the Dell web site and choose from a wide range of xeon based machines that can access 16Gb of memory. You can find Opterons with that much and more from IBM and HP. If you need that much memory its not hard to find among mainstream suppliers. I'm sure the motherboards they use are also widely available.