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Zantham · 08-26-07, 01:47 PM

The hypertransport bus (AMD) and the front side bus (Intel) both exist for the same reason, that is to provide intercommunications between
the CPU and RAM, the chipsets (it is common to see the Northbridge and Southbridge chipsets using Hypertransport, even on Intel based
systems), Hypertransport is even used to communicate between CPU cores (same as Intel FSB does).

Intels solution, the Front Side Bus, places a priority on high bandwidth. This is why we have seen a constant increase in RAM speeds,
SDRAM to DDR, then DDR2, now DDR3...PC-133 used to be considered overclockers RAM, now you can get RAM that is PC-10,000 and beyond. All
this plugged into a Front Side Bus that was 400, then 533, 800, 1066, and now 1333MHz. These front side bus speeds get real confusing
real quick...1333 is really 667, which is really 333. Intel 'quad-pumps' their front side bus to the CPU, but only 'double-pumps' to the
RAM, so technically a 1333 FSB CPU should only require DDR3-667, which in practise is not really enough bandwidth.

AMD however came up with the Hypertransport bus, which emphasizes a low latency solution over high bandwidth. Even with DDR2-800 being
the standard RAM (price for performance), even current AMD systems do not utilize anywhere near the bandwidth this RAM has to offer
(6.4GB/sec). In a benckmarking article I read a while ago, back when AMD X2-4000+ was fast and DDR2 had just started appearing, it was
found that AMD CPU's were more than satisfied bandwidth-wise with single channel DDR-400 (not even DDR2). DDR2 was bad for AMD systems
because instead of running at latencies as low as 2-2-2-5 like DDR, DDR2 ran at 4-4-4-12. AMD was forced to switch to DDR2 simply because
of Intel's success at marketing, causing DDR prices to rise while DDR2 prices fell due to supply and demand (Intel holding lion's share of
the market). AMD decided to adopt dual channel as well, again for similar reasons. Keep in mind AMD CPU's have sped up a lot since then,
so only the general principles hold true for this example. As AMD CPUs speed up to 6000+ and beyond, their RAM bandwidth requirements
speed up also. DDR3 is even worse, because its latencies are even higher than DDR2. Nowadays it is again possible to run DDR2 at 2-2-2-5
by buying more espensive RAM and lowering its latencies in your BIOS and testing for stability.

Intel will soon (2009?) be doing away with front side bus technology. They have adopted a strategy (ironically similar to Microsoft) where every 2nd generation of CPU is a refresh of current technology (Merom to Penryn, die size shrunk, faster FSB), then a new technology (Penryn to whatever the next one is called...spec so far seem to call for same die size, but different architecture). (May need to edit this paragraph later for accuracy)

So in the end, to bring this back on topic (apologies), my personal choice for RAM for an AMD system would be higher quality DDR2-800 (best price, more than enough performance), and then try to lower the latencies as much as possible. Also DDR2-800 is 'officially' supported on most boards.

Edit: Sorry for the formatting...typed in Notepad then copied over appears to insert inconvenient carriage returns into the document.

08-26-07, 01:47 PM	#15
Zantham 中国水兵 Join Date: Feb 2007 Location: Canada Posts: 283 Downloads: 63 Uploads: 1	The hypertransport bus (AMD) and the front side bus (Intel) both exist for the same reason, that is to provide intercommunications between the CPU and RAM, the chipsets (it is common to see the Northbridge and Southbridge chipsets using Hypertransport, even on Intel based systems), Hypertransport is even used to communicate between CPU cores (same as Intel FSB does). Intels solution, the Front Side Bus, places a priority on high bandwidth. This is why we have seen a constant increase in RAM speeds, SDRAM to DDR, then DDR2, now DDR3...PC-133 used to be considered overclockers RAM, now you can get RAM that is PC-10,000 and beyond. All this plugged into a Front Side Bus that was 400, then 533, 800, 1066, and now 1333MHz. These front side bus speeds get real confusing real quick...1333 is really 667, which is really 333. Intel 'quad-pumps' their front side bus to the CPU, but only 'double-pumps' to the RAM, so technically a 1333 FSB CPU should only require DDR3-667, which in practise is not really enough bandwidth. AMD however came up with the Hypertransport bus, which emphasizes a low latency solution over high bandwidth. Even with DDR2-800 being the standard RAM (price for performance), even current AMD systems do not utilize anywhere near the bandwidth this RAM has to offer (6.4GB/sec). In a benckmarking article I read a while ago, back when AMD X2-4000+ was fast and DDR2 had just started appearing, it was found that AMD CPU's were more than satisfied bandwidth-wise with single channel DDR-400 (not even DDR2). DDR2 was bad for AMD systems because instead of running at latencies as low as 2-2-2-5 like DDR, DDR2 ran at 4-4-4-12. AMD was forced to switch to DDR2 simply because of Intel's success at marketing, causing DDR prices to rise while DDR2 prices fell due to supply and demand (Intel holding lion's share of the market). AMD decided to adopt dual channel as well, again for similar reasons. Keep in mind AMD CPU's have sped up a lot since then, so only the general principles hold true for this example. As AMD CPUs speed up to 6000+ and beyond, their RAM bandwidth requirements speed up also. DDR3 is even worse, because its latencies are even higher than DDR2. Nowadays it is again possible to run DDR2 at 2-2-2-5 by buying more espensive RAM and lowering its latencies in your BIOS and testing for stability. Intel will soon (2009?) be doing away with front side bus technology. They have adopted a strategy (ironically similar to Microsoft) where every 2nd generation of CPU is a refresh of current technology (Merom to Penryn, die size shrunk, faster FSB), then a new technology (Penryn to whatever the next one is called...spec so far seem to call for same die size, but different architecture). (May need to edit this paragraph later for accuracy) So in the end, to bring this back on topic (apologies), my personal choice for RAM for an AMD system would be higher quality DDR2-800 (best price, more than enough performance), and then try to lower the latencies as much as possible. Also DDR2-800 is 'officially' supported on most boards. Edit: Sorry for the formatting...typed in Notepad then copied over appears to insert inconvenient carriage returns into the document.