800 vs 1066 question please

[AMDThunder]

Mobo: GA-EP43-DS3L
CPU: E6300

Both the mobo and CPU are listed as 1066 FSB. I'm currently running 3GB of G. Skill PC6400 Ram that I'll be replacing with 2X2GB sticks. Haven't decided on the brand yet, but G. Skill has been good to me so far. Question is, what's the benefit (if any) of going with the PC8500 vs. the PC6400? I've tried reading through the FAQ at the top, and reading through posts, but haven't had any luck finding my answer.

I think I understand that there won't be much of a performance boost moving to 1066 over the 800, but doesn't it make sense if the CPU and FSB are both running at 1066? Or maybe I'm not understanding correctly. If I'm at least understanding memory correctly, I believe I'll have to manually adjust the timings to get the PC8500 to run at 1066.

I'm not a complete noob. I've been building my own rigs for a while now, and have dabbled with, and sucessfully OC'd, with pretty good results. Unfortunately, the whole memory thing continues to elude me. I'm not currently OC'd, and probably won't until I replace my CPU. I've replaced everything in my box except memory and CPU.

Thanks in advance, and WOOT 500th post!!

 

[GhislainG]

Assuming quality modules with low latency, 1066 Mhz will improve performance from 0-1.5%. You can overclock good 800 Mhz memory yourself and probably get the same results.

 

[SpinachEater]

Yeah, agreed with above. I have DDR2 800 and I am pretty sure it is running a hair over 1000 MHz at the moment. My FSB is around 430 ish so I am using an odd ball ratio...I am not at my computer for the exact numbers but they are in the ballpark. If I didn't change my ratio it would be set to 1:1 and my RAM would run at 860 MHz otherwise.

In order to get your RAM frequency over 2x of your FSB you will need to adjust the ratio not the timings. You can change the timings and keep the same RAM frequencies....they are separate.

 

[Mondoman]

Essentially no benefit. The reason is that the 1066MHz FSB datarate is the full capacity of the FSB. The memory bus, however, runs in dual-channel mode (assuming you have pair of identical DIMMs installed in the correct slots), which means the individual DIMM datarate gets doubled. If you are running your DIMMs at DDR2-800 speed, the total memory bus datarate in dual channel mode is 2x800MHz = 1600MHz.

However, all data between the CPU and RAM has to go through the FSB, so it gets bottlenecked to the FSB's 1066MHz, no matter how fast you run your RAM. Thus, it's best to run your RAM modules at 1/2 the FSB datarate, which in your case is DDR2-533. 2x533MHz = 1066MHz, so it will exactly match your FSB throughput.

 

[AMDThunder]

which in your case is DDR2-533. 2x533MHz = 1066MHz, so it will exactly match your FSB throughput.

Ah, see, I'd completely forgotten about that. My mobo's max FSB is 1333, so my CPU is slowing me down as well since it's capped at 1066. My memory is running in dual channel, but it's automatically crippled by the slower FSB. Mobo says it can be tweaked to 1600 FSB when OC'd, but I'm wondering how detrimental that could be on an older CPU like I have.

Thanks for the input guys. Point taken though, no sense in buying anything higher than 800Mhz ram. Next build will probably require DDR3 anyway.

 

[Mondoman]

To the contrary, your e6300 is a great candidate for OCing. My e6420 is nominally a 1066MHz FSB CPU, but I just set my FSB to 1333MHz in the BIOS and voila! I've got a 2.66GHz CPU now instead of a 2.1GHz CPU. Since your mobo is rated up to 1600MHz FSB, you shouldn't have any problems from MB components at 1333MHz.

 

[AMDThunder]

Guess I'd forgotten more than I'd realized. I knew that somewhere in the recesses of my brain. Once upon a time, I had this one OC'd to 3.0. Guess it's time to do it again!

Thanks Mondo.

 

[tokyotech]

If you are running your DIMMs at DDR2-800 speed, the total memory bus datarate in dual channel mode is 2x800MHz = 1600MHz.

May I ask how you determine DDR2-800 to run at 800 MHz? Wikipedia says DDR2-800 runs at 400 MHz : http://en.wikipedia.org/wiki/DDR2_SDRAM

 

[GhislainG]

DDR2 at 800 Mhz is 400 Mhz x 2. That's why it's referred to as DDR2.

 

[Mondoman]

Normally, the BIOS setting uses the "800" number, not the "400" number. Also, I was talking about *datarates*, not raw bus frequency.