I was wondering, does the G5 have a VE in the same sense that the G4 does? I only ask because while Apple constantly harped on about the power of the VE with the G4 I've seen very little discussion about the VE with regards to the G5.
A little longer answer: Yes. The reason Apple haven't been whining and making so much noise about the VE of the G5, is that for G4, it was necessary to make use of it to make the CPU seem fast. With G5, it's not that necessary, and it does pretty well without. But it still kicks alot of butt when VE is used.
A little longer answer: Yes. The reason Apple haven't been whining and making so much noise about the VE of the G5, is that for G4, it was necessary to make use of it to make the CPU seem fast. With G5, it's not that necessary, and it does pretty well without. But it still kicks alot of butt when VE is used.
A bit more complex answer: The VMX (ibm name for moto's altivec) implementation IBM used in the PPC 970 is much closer in performence/clock cycle to the MPC 7400/7410 than to the latest generations. As this is a drawback (very little), they won't probably ever mention it. Anyway, the PPC 970 clock speed more than match this little problem.
A bit more complex answer: The VMX (ibm name for moto's altivec) implementation IBM used in the PPC 970 is much closer in performence/clock cycle to the MPC 7400/7410 than to the latest generations. As this is a drawback (very little), they won't probably ever mention it. Anyway, the PPC 970 clock speed more than match this little problem.
I think a simpler explanation is that the G5's big feature is "64-bit". Velocity Engine is old news and marketing likes to talk about new news. VE has some real advantages on the 970, however, including improving its somewhat lackluster per-clock integer performance. The huge memory bandwidth of the G5 also lets VE really shine.
please excuse my ignorance but If I understand you correctly the G4 VE and G5 VE are two different technologies. Does this mean that softwrae has to be rewritten to take advantage of the G5 and then that software also has to be rewritten to take advantage of the G5 VE? Am I right in assuming that software that is optimised for the G4 VE does not neccesssarily work for the G5 VE?
please excuse my ignorance but If I understand you correctly the G4 VE and G5 VE are two different technologies. Does this mean that softwrae has to be rewritten to take advantage of the G5 and then that software also has to be rewritten to take advantage of the G5 VE? Am I right in assuming that software that is optimised for the G4 VE does not neccesssarily work for the G5 VE?
They're two different implementations of the same specification, so code written for one will run on the other.
However.
There are a few AltiVec instructions for the G4 that are designed to work around the relatively poor bandwidth of its bus that hammer performance on the 970. The code runs, it just runs poorly. So in practice, AltiVec code does have to be tweaked for the G5. Also, the G4 allowed more different kinds of instructions to be dispatched simultaneously, and code that assumes it can do that will also suffer on the 970 (although not as badly as code with the first instructions, called "prefetch" because they are requests for data made before the data is needed).
Apart from those two issues, the two implementations of the Velocity Engine are compatible.
please excuse my ignorance but If I understand you correctly the G4 VE and G5 VE are two different technologies. Does this mean that softwrae has to be rewritten to take advantage of the G5 and then that software also has to be rewritten to take advantage of the G5 VE? Am I right in assuming that software that is optimised for the G4 VE does not neccesssarily work for the G5 VE?
thanx
Software that is written to take advantage of the G4 VE, will take advantage of the G5 VE, and the other way around.
Though, in some cases, you will hear that software runs very slow on the G5, and much slower than on the G4. It is not because the software is incompatible (then it wouldn't even run), it is usually because it is using some instructions (among them "vec_dst") that helps performance for the G4, but makes it slow down alot on the G5. However, it is a very trivial issue to work this around, and could usually be done in a very short time.
Comments
A little longer answer: Yes. The reason Apple haven't been whining and making so much noise about the VE of the G5, is that for G4, it was necessary to make use of it to make the CPU seem fast. With G5, it's not that necessary, and it does pretty well without. But it still kicks alot of butt when VE is used.
Originally posted by Zapchud
A little longer answer: Yes. The reason Apple haven't been whining and making so much noise about the VE of the G5, is that for G4, it was necessary to make use of it to make the CPU seem fast. With G5, it's not that necessary, and it does pretty well without. But it still kicks alot of butt when VE is used.
A bit more complex answer: The VMX (ibm name for moto's altivec) implementation IBM used in the PPC 970 is much closer in performence/clock cycle to the MPC 7400/7410 than to the latest generations. As this is a drawback (very little), they won't probably ever mention it. Anyway, the PPC 970 clock speed more than match this little problem.
Originally posted by Mac Force
A bit more complex answer: The VMX (ibm name for moto's altivec) implementation IBM used in the PPC 970 is much closer in performence/clock cycle to the MPC 7400/7410 than to the latest generations. As this is a drawback (very little), they won't probably ever mention it. Anyway, the PPC 970 clock speed more than match this little problem.
I think a simpler explanation is that the G5's big feature is "64-bit". Velocity Engine is old news and marketing likes to talk about new news. VE has some real advantages on the 970, however, including improving its somewhat lackluster per-clock integer performance. The huge memory bandwidth of the G5 also lets VE really shine.
please excuse my ignorance but If I understand you correctly the G4 VE and G5 VE are two different technologies. Does this mean that softwrae has to be rewritten to take advantage of the G5 and then that software also has to be rewritten to take advantage of the G5 VE? Am I right in assuming that software that is optimised for the G4 VE does not neccesssarily work for the G5 VE?
thanx
Originally posted by spooky
Thanx for the replies guys.
please excuse my ignorance but If I understand you correctly the G4 VE and G5 VE are two different technologies. Does this mean that softwrae has to be rewritten to take advantage of the G5 and then that software also has to be rewritten to take advantage of the G5 VE? Am I right in assuming that software that is optimised for the G4 VE does not neccesssarily work for the G5 VE?
They're two different implementations of the same specification, so code written for one will run on the other.
However.
There are a few AltiVec instructions for the G4 that are designed to work around the relatively poor bandwidth of its bus that hammer performance on the 970. The code runs, it just runs poorly. So in practice, AltiVec code does have to be tweaked for the G5. Also, the G4 allowed more different kinds of instructions to be dispatched simultaneously, and code that assumes it can do that will also suffer on the 970 (although not as badly as code with the first instructions, called "prefetch" because they are requests for data made before the data is needed).
Apart from those two issues, the two implementations of the Velocity Engine are compatible.
Originally posted by spooky
Thanx for the replies guys.
please excuse my ignorance but If I understand you correctly the G4 VE and G5 VE are two different technologies. Does this mean that softwrae has to be rewritten to take advantage of the G5 and then that software also has to be rewritten to take advantage of the G5 VE? Am I right in assuming that software that is optimised for the G4 VE does not neccesssarily work for the G5 VE?
thanx
Software that is written to take advantage of the G4 VE, will take advantage of the G5 VE, and the other way around.
Though, in some cases, you will hear that software runs very slow on the G5, and much slower than on the G4. It is not because the software is incompatible (then it wouldn't even run), it is usually because it is using some instructions (among them "vec_dst") that helps performance for the G4, but makes it slow down alot on the G5. However, it is a very trivial issue to work this around, and could usually be done in a very short time.
ARRRRRGH, Amorph!!!
Originally posted by Placebo
I think you can call the G5's Velocity Engine "disowned".
Not at all, it is discussed on Apple's G5 website and mentioned several times among the benchmarks they use.