Comparing Single 64-bit Processor vs. Two 32-bit Processors under Linux

[olodum]

I am running computationally intense simulations in fortran under linux-based environment (details below). Can anyone tell me how important it is to use a 64-bit processor as opposed to 32-bit? I am mainly interested in shortening simulation time. Also, how does performance on Athlon 64's, Opteron's and Intel Xeon / Itanium compare? Moreover, within a given category, what is the gain from each upgraded clock speed?

Simulation Details:
Nonlinear Partial Differential Equation, propagated forward in time stochastically via Cranck-Nicholson, or similar numerical scheme. Accuracy is important as correlations are investigated. Program written in fortran 77, cross-compiled with random number generator in C.

 

[ncage]

Olodum there is a lot of things to consider here so my answer would be.....it depends. Is the application coded to take advantage of 64 bit? Are the data types the programmer used 64 bit? Example did he program his integers as 64 bit integers or 32 bit integers? Its the most effecient to use varaibles the same size of your registers. Also depends on how good the compiler he used to compile the program. Will it be faster on two processors? This depends also. Did he program the application to take advantage of two processors (shared memory/semiphores)? Which processor type would be the best for this program is questionable too. Did he program it in a way that he requires lots of memory read/writes...if he did then it would help to have an athlon/opteron because of the integrated memory controller. Did he take advantage of sse/sse2/ss3? If he did it would get a boost by the sse implementation by intel. I think overall though the athlon would win because of the great FPU unit in AMD processors. How much would clock speed help? That all depends too...did he code the application so it is i/o limited...then a faster processor would just be waiting on I/O. Your question is just to hard to answer forsure without further analysis of the factors. If you want a processor that would give you top speed though without further analysis and you don't want to spend the money on a high end server i would say stick to the Athlon 64 X2 line of processors.

ncage