[Nobody]

Hi,
I've read a couple of times that you can't use Virtual PC on a G5. Why is that? I want to buy a G5 and I was thinking of also getting VPC.
Merry Christmas!

[mystery_stain]

Apparently they were trying to maximize performance by taking advantage of some kind of G4 CPU optimization, but it used a G4 CPU feature which is not present at all on the G5, or something like that, so the program can't run. The conspiracy crowd says it's because of Microsoft, but it was programmed that way before Microsoft bought Virtual PC.
But there is a rumor that says Microsoft might be announcing a G5 Virtual PC in a couple weeks, which would further annoy the conspiracists who thought MS bought VPC to kill it.

[Nobody]

Ok, thanks mystery stain /forums/ubbthreads/images/graemlins/grin.gif Lets hope MS does bring out a G5 version of VPC.
Marry Christmas,

[d00d]

It's because G5's don't have a little-endian emulation mode like G4's. One of the core differences between PowerPCs and x86 processors is that PowerPCs are big endian and x86 are little endian. Essentially, the most significant portion of a bit string is stored first in big endian. In little endian, it's at the end. For example, the internet for the most part is little endian in the way domain names are handled. For sports.yahoo.com, the most important part of that address is the end, .com which is the largest separator. Without this translation being present in the processor, this has to be done in another way (most likely at a large speed cost). There is no way the current version will work on the current G5 processor.

[Nobody]

Thanks for the info d00d. I really appreciate it.
Merry Christmas.

[Praxis]

So the G5 VPC will probably run slower than than the G4 version?
Dang.

[mystery_stain]

What makes you think that? I would think that any performance benefit from G5 compatibility would far outweight that single lost G4 optimization.

[d00d]

That's more than a minor optimization. The amount of code to correctly workaround this problem could be substantial. Instead of loading data directly into the registers as they are generated by programs, they might have to be translated. This optimization is central to the core operation of the emulation.
Now, I don't know if there are any facilities in the G5 processor that could be substituted for this functionality, nor do I know if Microsoft will come up with a creative way to address the problem. This may yield a smaller performance hit. However, it nearly ever happens that a workaround for something done in software is faster than something done in hardware (hence why VirtualPC is pretty much incapable of running 3D games, the emulated video card just isn't as fast as an actual hardware card).
Whether the sheer processor and bus power of the G5 will be able to make up for this shortcoming has yet to be seen. However, I think the performance per megahertz of the G4 version will be greater than the G5 version.