HOHOH said:
I have a experiance in XP(32bit) and Vista(64bit).
CPU : AMD Athlon 64 X2 4400
RAM : 4 GB
I applied to simulate waveguide to coaxial adapter by hfss 10.0.
The result of hfss in XP(32bit) is 2 times fast more than vista(64bit) condition.
It's a simple comparison of result and I don't know accuracy method for comparison.
Please recommend method. I can re-try evaluation.
I think there is a popular misunderstanding that 64-bit processors are faster for a lot of reasons. Some people think that they perform more multiplications per cycle because they handle a larger accumulator size. Other people think that there are special features in the way the ALU works.
In the latest class of 64-bit processors, there are a lot of things that work to provide faster analysis:
- Bigger L2 Cache size. This makes a very big difference in that you keep more data closer to the CPU where intense calculations are taking place. Less fetches have to be made to the memory to move data close to the CPU for processing.
- Better Front-Side Bus (FSB) - New FSBs are faster and more efficient. For EM simulation, faster FSB has a big effect on overall processing speed.
- Some EM simulators are starting to use more advanced features in the new 64-bit processors that were not available in older processors.
- Faster clock speeds. Processing time in EM simulators scale more or less with the clock speed.
Changing to a 64-bit OS shouldn't change any of these factors.
I really agree with Azulykit that if you have 2 GB of RAM on your computer, and you have solver process that requires around 1.5 GB of RAM (or maybe a little larger) you eventually get to the point where the OS cannot hold everything in RAM; it has to "borrow" virtual RAM space from the hard disk. This is what we sometimes call "Swapping to disk." And when it starts to happen, you might as well kill the job and rework the model, as has been stated already. Swapping to disk can slow the job 100x or more because instead of accessing RAM, your computer is now trying to access some of that memory through your very slow hard disk controller (at least it's very slow compared to RAM access).
Slower simulation times on Vista can be from several reasons:
1. Vista, as an OS, requires a *lot* more basic RAM just for the OS than did Windows XP. So the largest effective job you can run is probably smaller on your PC under Vista than it was under XP because you simply have less RAM space left to use. Vista is very wasteful of RAM!
2. Vista also has a few more things going on in the OS than the older OSs.
3. HFSS might not be optimal for Vista. A lot of software developers are finding that Vista is forcing them to change a lot of stuff to be properly compatible. (Does Ansoft actually say that they support 64-bit Vista in this release? I don't think so, so this might be part of the problem. While the software might run in Vista/64, it isn't likely to have been optimized for it.)
You might want to try benchmarking other applications besides just HFSS. This might tell you if the problem is HFSS, or if you are finding that your computer simply runs slower under Vista/64.