On Jan 28, 2004, at 11:09 AM, Robin Ashe wrote:
There's nothing stopping them from designing a new northbridge, or even building it into the CPU like the A64.
Except for the fact that precious little happens in the PPC northbridge and CPU world.
The problem lies in the fact that at
best you get 60% extra performance for each extra CPU. So 4 CPUs would give
at best 220% of the performance of a single CPU. Not really worth it
considering the extra power.
Something else that's interesting to note about the G4s is that somewhere
around the 867MHz mark Motorola decided to trade clockspeed for efficiency.
So apple was finally able to break the 1GHz mark but there wasn't a
significant performance gain. (Which is what Intel has been doing with the
P4 for a long time). So that brings the extra performance out of the speed
increase even lower.
Bus bandwidth is the big limiting factor and for years Motorola has been behind the capabilities of leading edge SDRAM. The G5 northbridge at least can keep up with DDR. I believe even the very most recent G4 frontside busses can't even keep up with DDR.
What the G5 seems to be is a new architecture that supports higher clock
speeds more than anything else.
Agreed! And it also can take advantage of DDR memory speeds.
Of course that is a good thing, as higher
clock speeds means better performance, but I think an Alpha-like focus on
efficiency would be preferable. 64-bit doesn't offer much of an advantage
either, as it's been demonstrated that it is slightly slower than 32-bit
anyway (but not by a significant margin).
Yes, all else being equal, a 64 bit computer running in 64 bit mode has to pass 8 byte memory addresses as opposed to 4 byte memory addresses. It has to move more data to get things done.
Paul
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