Ok, I don't have any particular problem, I've just been having difficulty understanding how the different types of RAM work. Here is what I think I know and if anyone could correct me, I would greatly appreciate it. Old-School SDRAM had very straight forward specifications. It had a clock speed and higher was better and woopdedoo things were easy. DDR: Eventually they came out with DDR RAM which enabled RAM to send data on both the voltage upswing and downswing of a single clock cycle. Aka basically it enabled transmission of two pieces of data per clock cycle as opposed to just one. Here things are still pretty easy because DDR is inherently better than old SDRAM. So DDR 100 RAM is obviously better than 100 Mhz SDRAM DDR2: is a fake technology...sort of. They double the size of the prefetch buffer, which, as far as I know is just the place the FSB looks at on the RAM to take info back to the CPU. The RAM is responsible for filling the prefetch buffer with the correct data. However, the FSB can only take 1 thing at a time, so in turn they also double the speed of the FSB. Because the FSB is operating at twice the speed as the RAM in the DDR2 scenario, it can deliver X and come back and get Y in the same time as it took to get one piece of data in the DDR scenario. Cool right? double the performance right? not necessarily: As I understand it, the problem lies in the fact, that before the FSB can deliver the information back to the CPU, the RAM now has to find 2 things instead of 1. This results in an increase in something that I dont completely understand called CAS latency - aka the time it takes for the RAM to look things up. This time is just significant enough, that DDR2 400 RAM (which is clocked at 100 Mhz), won't necessarily outperform DDR RAM at the same clockspeed, because of the increased CAS latency. However, where DDR2 does get its bonus is in the fact that is is capable of reaching MUCH higher clock speeds than DDR, thus increasing overall throughput if you make the RAM fast enough. So finally to my question: Manufacturers continually advertise "woohoo we're selling DDR2-800 RAM," however this would require a 1600 Mhz FSB to fully utilize the speed of the RAM correct? Also, since the latest and greatest FSB speed is 1333 Mhz and most of the motherboards utilizing this latest and greatest FSB are moving towards DDR3 RAM, is there really anypoint in getting DDR2 RAM above 667 (667x2 = 1333). Thanks for any re-education you can supply me
There's a slight confusion on how you see DDR. While the DDR clock may be 100MHz, it's rated as 200MHz with the DDR tag. So DDR2-800 runs at 400MHz, not 1600MHz. Don't quote me on this, but my gut feeling is that DDR started off with DDR-200 instead of 100 to distance itself from SDR SDRAM, which tops out (officially) at 133MHz, per JEDEC standards.
