In response to my earlier posts the following comments were made:
thatwendigo said:
Then you really don't understand how either HyperTransport or the Apple FSB work, since both are basically the same thing.
AidenShaw said:
Opteron/Athlon have an on-chip FSB/memory controller that runs at clock speed.
HT is an I/O bus and a cache-coherency bus for MP - it is not the memory (FSB) bus.
Well, I think you two "experts" need to get together since you both seem to want to correct my "errors" but you're basically saying the opposite to one another.
As I've said before, I don't think you can directly compare the FSB designs between the Athlon 64 and the Power Mac G5. That's probably why the two of you (thatwendigo and AidenShaw) seem to disagree on what the FSB is on the Athlon 64 (is it the memory interface or is it the system bus?). I think in the more traditional sense it is really what is called the system bus and AMD calls the Athlon 64's HyperTransport link the system bus. And certainly, the 1GHz bus that runs between the G5 and the Power Mac's system controller is both the system bus AND the FSB.
As far as what a FSB is, here is one definition I found in an article that was published on TechNewsWorld.com
"As one of the most important processing channels, the frontside bus is the primary interface that connects a microprocessor to other system devices. Typically, the FSB allows the processor to communicate with main memory (RAM), the system chipset, PCI devices, the graphics card and other peripheral buses."
While this definition fits well on the Power Mac G5 you can see that the design of the Athlon 64 doesn't really fit here. And that's always been my point (which thatwendigo seems to want to disagree with).
Interestingly, this article then goes on to discuss the various differences in the methods that Intel, AMD, and IBM (G5) are pursuing to break what they termed the "Frontside Bus Bottleneck." Hint, although there are similarities it's apparent that IBM and AMD are not pursuing the same track.
Here is the link:
http://www.technewsworld.com/story/31594.html
Or how about this (from Geek.com):
"Front Side Bus (FSB) - The speed of the bus connecting the microprocessor, its chipset, and connected main memory. In architectures where the processor interacts directly with main memory, the definition of a singular front side bus is less clear. In such a case you would have to specify two FSB speeds, one for the connection to main memory and one for the connection to the processor chipset."
Which really, I guess, directly supports my position about trying to compare the Athlon 64 "FSB" to the Power Mac G5.
thatwendigo said:
I'm not at all certain why it would be "nice" if the G5 supportes slower bus multipliers, especially since bandwidth is one of its few advantages.
Well, since Arstech specifically asked about the available bus multipliers when they interviewed IBM's Peter Sandon (chief architect on the PPC970) I think that probably indicates that at least some people think that bus multipliers other than 2X are potentially useful. When I went back to this article I found that Peter Sandon said that the "processor design" supports bus multipliers of 2, 3, 4, and 6. However, I think it was unclear whether the PPC970 actually implemented those multipliers (i.e. the design could support them, but it may not be implemented in the 970).
Here is the link where they discuss the bus multipliers:
http://arstechnica.com/cpu/03q2/ppc970-interview/ppc970-interview-2.html
Well, I guess I rest my case (or arguments).