hmurchison
2004-07-20, 17:33
Ok love'em or hate'em Rambus has some cool stuff coming and I think it may affect future Macs.
Rambus recently announced a memory controller that supports DDR, DDR2 and their new XDR. This is cool, "one memory controller to rule them all". This means the same memory controller could scale as follows.
eMac- Rambus Controller--> DDR
iMac-Rambus Controller--> DDR2
Powermac-Rambus Controller--> XDR
The Controller (http://www.rambus.com/introducingddr/ )
Try the nifty Bandwidth Calculator (http://www.rambus.com/supportgroup/)
Here's a little tidbit on why Rambus XDR is special
Key to XDR DRAM's draw is its high bandwidth per pin. Using a 400MHz clock, XDR can transmit eight data bits per clock (octal data rate) attaining a 3.2GHz/pin data rate. An 8-bit interface can transfer 3.2GBs/sec, and a 32-bit interface hits 12.8GB/sec. Tack two 32-bit "XDIMMS" together and you reach 25.6GB/sec at 3.2GHz signaling. Rambus expects to quickly move to 6.4GHz/pin signaling, so if you expand to a 128-bit interface at 6.4GHz/pin, you can reach 102.4GB/sec. This is far beyond speeds on DDR roadmaps. Rambus attains such speeds using three key technologies: Differential Rambus Signaling Levels (DRSL), FlexPhase technology (to compensate for timing errors), and octal data rate signaling mentioned previously. You can check out Rambus XDR info on their site for technical details.source: extremetech.com
Now keep in mind that GPU like the new Nvidia 6800 and ATI XT800 use GDDR3 which currently does about 50+ GBps throughput. Samsung is going to have a 1.4Ghz(2.8Ghz effective) part by the end of this year that supports 89GBps . The Rambus XDR may be competitive in this area.
Frankly the DDR2 roadmap isn't all that impressive. DDR2 667hz for 2005 and maybe 800 by 2006. That gives us PC6400 possibly.This in a Dual Channel config would give you 12.8GBpss throughput. Using the calculator linked above it shows that
DDR- You'd need a 256bit memory interface with 32 componetns.
XDR- You'd need a 48bit memory interface with 3 components.
Looks like Apple might want to give themselves the most leverage with memory by keeping options open. XDR might just wipe DDR off the map. You can call Rambus a lot of things but with RDRAM they were indeed expensive but the benchmarks showed that bandwidth was indeed king. Latency wasn't hot then but look at DDR2 and it's poorer latency compared to DDR. Without a huge increase in bandwidth DDR2 is not a sure thing.
Rambus recently announced a memory controller that supports DDR, DDR2 and their new XDR. This is cool, "one memory controller to rule them all". This means the same memory controller could scale as follows.
eMac- Rambus Controller--> DDR
iMac-Rambus Controller--> DDR2
Powermac-Rambus Controller--> XDR
The Controller (http://www.rambus.com/introducingddr/ )
Try the nifty Bandwidth Calculator (http://www.rambus.com/supportgroup/)
Here's a little tidbit on why Rambus XDR is special
Key to XDR DRAM's draw is its high bandwidth per pin. Using a 400MHz clock, XDR can transmit eight data bits per clock (octal data rate) attaining a 3.2GHz/pin data rate. An 8-bit interface can transfer 3.2GBs/sec, and a 32-bit interface hits 12.8GB/sec. Tack two 32-bit "XDIMMS" together and you reach 25.6GB/sec at 3.2GHz signaling. Rambus expects to quickly move to 6.4GHz/pin signaling, so if you expand to a 128-bit interface at 6.4GHz/pin, you can reach 102.4GB/sec. This is far beyond speeds on DDR roadmaps. Rambus attains such speeds using three key technologies: Differential Rambus Signaling Levels (DRSL), FlexPhase technology (to compensate for timing errors), and octal data rate signaling mentioned previously. You can check out Rambus XDR info on their site for technical details.source: extremetech.com
Now keep in mind that GPU like the new Nvidia 6800 and ATI XT800 use GDDR3 which currently does about 50+ GBps throughput. Samsung is going to have a 1.4Ghz(2.8Ghz effective) part by the end of this year that supports 89GBps . The Rambus XDR may be competitive in this area.
Frankly the DDR2 roadmap isn't all that impressive. DDR2 667hz for 2005 and maybe 800 by 2006. That gives us PC6400 possibly.This in a Dual Channel config would give you 12.8GBpss throughput. Using the calculator linked above it shows that
DDR- You'd need a 256bit memory interface with 32 componetns.
XDR- You'd need a 48bit memory interface with 3 components.
Looks like Apple might want to give themselves the most leverage with memory by keeping options open. XDR might just wipe DDR off the map. You can call Rambus a lot of things but with RDRAM they were indeed expensive but the benchmarks showed that bandwidth was indeed king. Latency wasn't hot then but look at DDR2 and it's poorer latency compared to DDR. Without a huge increase in bandwidth DDR2 is not a sure thing.