The Logic Off Topic list

Iwrote:
>At 09:43 PM 13/08/02 -0400, you wrote:
>>>The most significant improvement with regard to running Logic on these
>>>new
>>>machines would seem to be the improvement in the memory bandwidth
>>
>>- faster bus
>>- faster type of RAM
>
>The FSB speed change and the RAM change boil down to the same thing -- DDR
>RAM instead of SDRAM. Now the G4 has a similar FSB/memory to the Athlon XP
>and the P4 with DDR. P4 with RDRAM is still the fastest memory interface
>but RDRAM is still expensive. The most significant improvement is that the
>memory bandwidth has gone up by 150% to 2.7 GB/sec. 

Oops! -- I credited Apple with providing the memory interface on the CPU to
use all this extra bandwidth.
At http://mosr.com/ they are saying it ain't so:

> The new 1.25GHz chips are, unfortunately, just upclocked PowerPC 7455 
>processors, not the PPC 7470s hoped for by the grapevine. This is a 
>dangerous flaw, because the PPC 7455 cannot take advantage of DDR memory -- 
>as on the Xserve, the new PowerMacs will be limited to 1.3GB/s actual 
>processor bandwidth despite 2.7GB/s memory bandwidth on the two high-end 
>models.

NVidia Nforce chipsets for the Athlon do something vaguely comparable. They
have dual 2.1GB/sec buses to DDR giving "in theory" 4.2 GB/sec memory
bandwidth. Trouble is,  the Athlon XP CPU to memory interface can only deal
with 2.1 GB/sec of data. If NVidia go ahead and make dual Athlon chipsets
(as they are rumoured to be doing soon) the dual banks of DDR will actually
confer some advantage. Intel will offer Dual DDR for P4 with the GraniteBay
chipset later this year. 

Regards,
Murray