FSB question

[kevbo]

Ok, I'm no apple fan, but I'm just wondering if anyone knows the details about the G5's 1 Ghz bus.

Intel's bus is 200 Mhz 'Quad Pumped' to get their 800 Mhz number and Amd's bus is 200 Mhz doubled to get their 400 value.

Does anyone know what the G5's 1 Ghz bus actually is? Do they work the same way and 'pump' it to get a bigger value? I have no idea how they work but it would seem stupid to have an actual 1 Ghz bus and a multiplier of 2 to get the 2 Ghz processor (I'm assuming they work the same way with fsb and multiplier). I'm guessing maybe a 250 Mhz bus??

And I'll just finish off by saying again that I'm not a big apple fan, so please don't throw large objects at me. I'm just curious and I'd be afraid to post on an apple message board....yikes...
Thanks

 

[phsstpok]

I didn't know the answer but you made me curious.

According to the specifications the G5 FSB is DDR technology (see link at end). This makes sense since the 1.6 Ghz, 1.8 Ghz, and 2.0 Ghz G5's have quoted bus speeds of 800 Mhz, 900 Mhz, and 1000 Mhz, respectively. Apple just ups the bus speeds for the faster models. And yes, that would be a 2X multiplier.

8 GB/sec per processor of potential bandwidth is d*mn impressive but with only dual channel DDR (PC2700 or PC3200) wouldn't the G5 be severely bandwidth starved?.

Specifications Link
<A HREF="http://www.apple.com/powermac/specs.html" target="_new">http://www.apple.com/powermac/specs.html</A>

<b>56K, slow and steady does not win the race on internet!</b>

 

[lhgpoobaa]

one would think yes... i thoguh that the mac was doublepumped actually.

<b>I am not a AMD fanboy.
I am not a Via fanboy.
I am not a ATI fanboy.
I AM a performance fanboy.
And a low price fanboy.
Regards,
Mr no integrity coward.</b>

 

[phsstpok]

That's what a DDR bus is, "double pumped".

<b>56K, slow and steady does not win the race on internet!</b>

 

[kevbo]

Why is the intel quad pumped then? Is it because of dual channel DDR?

And also, if the G5 is double pumped it would be 500 Mhz *2 to get the 1 Ghz right? Still a 500 Mhz bus compared to 200 for intel and amd it quick...

<P ID="edit"><FONT SIZE=-1><EM>Edited by kevbo on 09/22/03 02:17 AM.</EM></FONT></P>

 

[phsstpok]

The memory architecture is separate from bus architecture.

Quad data rate means data is transfered four times per clock pulse. With double data rate (DDR) it's twice per clock. This can apply to anything, buses, memory system. It's the same concept with AGP 2X and 4X.

The P4 may have a quad data rate bus but the memory system isn't. As you know the choices of memory subsystem for P4 are SDRAM (or was a choice when the Willamettes were around), DDR (single channel), Dual DDR, and RDRAM.

Dual DDR (200mhz, PC3200) is a good match for P4 because the bandwith is exactly the same as that of a 200 Mhz QDR bus.

As for G5 bus, 1000 mhz effective would make it a 500 mhz bus clock.

<b>56K, slow and steady does not win the race on internet!</b>

 

[pIII_Man]

seems to me that the g5 would be very limited by even dual ddr, a 6.4gb/s memory archetecture with a 8gb/s bus...almost like running single channel ddr with a p4. I think apple is just going for the "WOW" factor here showing that they have faster bus speeds than amd or intel...also looking at the specs these have properties that look more like entery level servers than home computers, (64 bit pci, pci-X ).


Proud owner of DOS 3.3 <P ID="edit"><FONT SIZE=-1><EM>Edited by piii_Man on 09/22/03 03:22 PM.</EM></FONT></P>

 

[HardWareBoss]

Not the ole Wow factor. I like it. New name for apple.

 

[phsstpok]

I made an assumption. Because Apple states you must install DDR memory in pairs I assumed it was dual channel memory. Perhaps the memory in pairs is a requirement of the 64-bit architecture. I don't know.

The claims of speed seem even more exaggerated when you look at the white papers. Apple starts talking about 16 GB/sec bandwidth using independent buses for the dual processor models of PowerMac G5.

Now we're talking about serious starvation.

PCI-X? Really? Is that going to survive once we start seeing PCI Express? or is PCI-X going the way of ISA, EISA, Micro Channel? (Sorry OT).

<b>56K, slow and steady does not win the race on internet!</b>

 

[pIII_Man]

Not sure, but pci-x is a 64 bit 133mhz bus, this would yeild an 8.533gb/s transfer, i dunno sounds very high to me...i must be missing something there <b>edit: stupid me, forgot to divide by 8, it would be 1066mb/s</b>. The good thing about pci-express is that it uses very small slots even the 8x or 16x slots should be about the same size as a agp or pci slot, where pci-64 is almost like 2 pci slots joined together reminds me of good 'ol vesa.

Ya i think its dual channel, they said 6.4mb/s max memory bus transfer. The mac is supposed to have dual indipendent buses, but i am kind of lost because no matter how many buses you have i would think each bus is still using the same main memory so Apple does not really capitalise on this feature, would be just as if both shared the same fsb. I am really starting to think this will be an extremely memory starved archetecture (just as you have noted).

On another note...i read through apples cpu spec sheet... more like a propoganda campeign, jeez look at a p4 spec sheet and compare it to that, shesh.


Proud owner of DOS 3.3 <P ID="edit"><FONT SIZE=-1><EM>Edited by piii_Man on 09/22/03 06:49 PM.</EM></FONT></P>

 

[pIII_Man]

Sorry to say but from my opinion just by reading the "technical specs" (laugh) it seems that apple is ALL about marketing. In their little spec sheet they showed benchmarks (first time i have ever seen that in a spec sheet) but they did not really go very in depth into system specs, it was 3.0ghz p4...ok...was it running on a pc133 bus? with 32mb of memory?


Proud owner of DOS 3.3