20081013, 02:49  #1 
Oct 2008
2^{2}×3 Posts 
64bit prime 95
Does using the 64bit binary of Prime95 significantly change the speed of the program?

20081013, 03:04  #2 
P90 years forever!
Aug 2002
Yeehaw, FL
5^{2}·307 Posts 
No

20081013, 03:19  #3 
Oct 2008
2^{2}×3 Posts 

20081014, 04:52  #4 
Jun 2003
153_{10} Posts 
The 64 bit version of Prime95 used with the 64 bit version of Windows XP does trial factoring twice as fast as the 32 bit versions of the same software.

20081014, 15:04  #5 
Oct 2008
1100_{2} Posts 

20081015, 18:18  #6 
Jun 2003
3^{2}×17 Posts 
I don't have any experience with Linux (either the 32 bit or 64 bit distributions).
Consequently, I can't help you there. For the windows environment I can provide some additional information and some history which might be helpful to you. When AMD extended the X86 ISA from 32 bits to 64 bits, they added 8 general purpose registers to their X86 hardware. However, these GP registers are only available for 64 bit CPUs running 64 bit operating systems. George was able to make use of these extra registers for trial factoring when he created the 64 bit version of Prime95. Consequently, Prime95 (64 bit) factoring on Windows XP (64 bit) is about twice as fast as Prime95 (32 bit) factoring on Windows XP (64 bit) or Windows XP (32 bit). Unfortunately, George, wasn't able to speed up his Prime95 (64 bit) LL code like he did for his trial factoring code. Last fiddled with by RMAC9.5 on 20081015 at 18:19 
20081015, 23:20  #7 
"Lucan"
Dec 2006
England
2×3×13×83 Posts 
It's frustrating that doubling the speed of trial factoring means
that it becomes profitable for only one more power of 2. Last fiddled with by davieddy on 20081015 at 23:38 
20081016, 00:33  #8 
"Richard B. Woods"
Aug 2002
Wisconsin USA
1111000001100_{2} Posts 
Look at the bright side: TF to one more bit level means that P1 after unsuccessful TF has a lower probability of finding a factor, for a given set of B1/B2 limits, so Prime95 will calculate that it is less worthwhile to do the P1, so it will use lower B1/B2 limits than it would have if the TF had been done to only a lower powerof2. _There's_ your speedup!

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