DDR2/DDR3, HT1.0/HT3.0 -- compromise ?

[banibratadutta]

Hi,

Some fundamental questions.

Q-1. My understanding is that for extracting the best benefit of DDR3, I need 3 symmetric memory sticks. If so, then can I expect any difference in performance between these 3 scenarios --
a. Have 2 DDR3 sticks (instead of 3) in a DDR3 supported MoBo / proccy
b. Have 2 DDR2 sticks in a DDR3 supported MoBo / proccy
c. Fall-back on a DDR2 (only) supporting proccy and use a pair of DDR2 sticks

Q-2. My understanding is that HyperTransport is used for CPU - GPU, or CPU - CPU communication in most typical desktop Mobo's, and not for anything else. If that is correct, and I do not intend have an add-on GPU, or use the on-board GPU (no gaming or other 3D work), does not having HT3.0 (instead having HT1.0) have any performance impact in any other way ?

PS> If someone (moderator?) feels that this thread might get better response in "Highly Technical" forum, kindly let me know.

regards,
BD

 

[tynopik]

Q-1. My understanding is that for extracting the best benefit of DDR3, I need 3 symmetric memory sticks.

false, that's based on the number of memory controllers the cpu has, not whether it's DDR2 or 3

most CPUs are dual channel except 1366 which is tri channel

that said, it really doesn't matter if you optimize the channels or not, the differences are so miniscule, you need a benchmark to tell them apart.

Q-2. My understanding is that HyperTransport is used for CPU - GPU, or CPU - CPU communication in most typical desktop Mobo's, and not for anything else. If that is correct, and I do not intend have an add-on GPU, or use the on-board GPU (no gaming or other 3D work), does not having HT3.0 (instead having HT1.0) have any performance impact in any other way ?

hypertransport is AMD's branded bus for inter-cpu/motherboard communication, basically you don't need to worry about it

PCIe on the other hand is what is used for graphics card (or any other card you plug-in plus some onboard peripherals)

all PCIe devices from 1.0 to 3.0 are fully backwards compatible (in theory), working at the lower speed of course. but again, the differences are usually so small you don't need to worry about it

especially if you're not using any 3D capabilities, even PCIe 1.0 x1 (one channel), the slowest possible PCIe implementation, is more than enough

 

[VirtualLarry]

You cannot run DDR2 in a DDR3 mobo. The mobo's physical slots are designed for either DDR3 or DDR2. Just because the CPU's memory-controller is bi-compatible, doesn't mean the mobo is. What it means is, you can drop an AM3 CPU into an AM2+ (DDR2) or AM3 (DDR3) mobo.

Also, the only CPU socket that uses tri-channel DDR3 is the 1366 socket, X58 chipset. All other mobos that use DDR3 are dual-channel.

 

[mfenn]

The number of DIMMs you "need" to have is determined by the memory controller, not the memory technology. There are dual-channel controllers that use both DDR2 and DDR3. While a triple channel DDR2 controller could theoretically be made, currently only the Intel X58 chipset implements triple-channel in DDR3 form.

HT is pretty much only used for communication between the CPU and chipset on a single-processor motherboard. The GPU communicates with the chipset via PCIe. That being said, since the memory controller is on the GPU, and memory requests eventually need to go over the HT link. Even the slowest form of HyperTransport is is approximately equivalent to a x8 PCIe 2.0 slot, which is plenty for any current GPU.

 

[banibratadutta]

@tynopik, @VirtualLarry, @mfenn ... thanks a ton folks ! The thread turned out to be majorly educational for me. Thanks for the clear and detailed explanation.