I don't get 975X FSB MHz..please someone enlighten me :)

[lukx]

Can somone explain me FSB speed thing. Let's take for example ASUS P5W DH Deluxe.

I can reed in specs:
"maximum 8GB dual-channel DDR2 800/667/533 architecture, 1066/800 FSB (front-side-bus). "

So when I get 533 DDR2 memory it isn't the fatses solution right?
I should get 800 to have full potential from this mobo.
So memory 1066 is just for overclocing. But what about this 1066/800 FSB if specs say that max memory is 800 not 1066. I'm stupid. Please help.

Finally if I don't decide to OC and want to run everything at stoc speed (ram, cpu etc) I sould get 800 ram 667 or 533?

 

[eelw]

C2Ds use 1066MHz FSB which is quad pumped. So you really only need 266MHz to match the speed. DDR memory, data is transferred on both the rising and falling edge of the cycle. So DDR2 533 is actually only running at 266MHz. And if you're not planning to overclock, DDR2 533 or PC4200 memory is all you need.

The 800 FSB is referring to older P4s and PDs.

 

[wgoldfarb]

I am a complete newbie at this, and I actually had a very similar question in the forum a couple of days ago, but I had understood it a little different, and I probably got it wrong.

In my original question I had looked at the P965 Express Chipset, where the bandwith between the DDR2 and the Memory Controller on the chipset is 12.8 GB/s. Since this is dual channel each channel can use 6.4 GB/s = PC 6400 = DDR 800 = 400Mhz. So, it seems that even though the system clock runs at "only" 266 MHz, the RAM can actually communicate with the CPU at a frequency of 400 MHz (and thanks to phile I now understand about memory dividers, which seems to be what is happening here). Even without overclocking, it sounds as if you could indeed benefit of using DDR2 800 in a P965 MoBo. Is this all correct?

 

[lopri]

No. RAM doesn't directly communicate w/ CPU on P965/975X. It has always travel the NB via FSB to CPU. So theoretically 1:1 is the optimal memory speed and as eelw said, under stock speed DDR2-533 (266MHz) is all you need. Basically you want to match the DDR2-XXX with your FSB (which is XXX/2). Now if your board and memory are capable, you can overclock the memory itself using dividers - In theory it should just be waste but in practice it raises the performance ever so slightly. It's because the FSB subsystem isn't perfect and there always a chance for CPU to be idle due to various reasons. If your memory is faster running the chance of CPU being idle will get smaller therefore the performance increase. But it's really not that big and you'll probably only notice in benchmarks. (e.g. Sandra)

 

[lukx]

okey, so if I'm not planing to OC, any memory higher then 533 is simple waste of money?

 

[lopri]

I'd get DDR2-800. These are not too expensive now for a 2GB set ($200~$240), and another thing to remember is that when you downclock these DDR2-800 to DDR2-533, you're almost guaranteed of tighter timings and lower voltages, which never hurt.

 

[lukx]

hmmm, but in this article it's stated that 533 is running sync with fsb and it's somehow better : http://www.madshrimps.be/?action=getarticle&articID=472

 

[lopri]

That depends on the apps but it's certainly possible that 1:1 can achieve better results than running memory faster. But one thing for certain is that given the same memory frequency, tighter timings are always better. (3-3-3>4-4-4)

 

[lukx]

thank lopri, but is is for sure that 800 downclocked to 533 will have tighter timings. ANd my another question, how is it that asus put in spects 800 memory? DOes it means that when I put 800 memory into mobo it will OC CPU by itself? Or just memory will run faster and CPU will run at stoc speeds?

 

[lukx]

oh and if I would get Corsair Twin2X DDR2 2x 1GB 1066 MHz CL5-5-5-12 and will decide to tun it at 533 will it also have tighter timings? Or if decide to run it at 800 will it have CL4 or as 1066 CL5?

 

[lopri]

No. When you first boot the board will load the SPD on the memory sticks (which is like idiot-proof safe timings). So depends on how SPD is programmed on certain modules, the results will vary but most likely it'll be something like DDR2-533 @5-5-5. (i.e. very loose timings) Then uopn selecting "Manual" instead of "Auto" on JumperFree/Chipset section, you now can select dividers and timings per your taste/your modules' capability. For instance, @266 FSB you'll be able to select among following dividers.

DDR2-400 (4:3=FSB:Memory)
DDR2-533 (1:1)
DDR2-667 (4:5)
DDR2-711 (3:4)
DDR2-800 (2:3)
DDR2-889 (3:5)
DDR2-1067 (1:2)

Available dividers will vary according to FSB. At stock speed (266FSB), as long as your memory is capable most of the dividers will probably work. But as you raise the FSB, you will gradually have to lower the ratio and eventually past 360~370FSB only 1:1 will work.

Check this excellent guide by Gary. Everything you're curious about is superbly explained there.

http://www.anandtech.com/mb/showdoc.aspx?i=2797&p=3

 

[wgoldfarb]

I was not the OP but I had very similar doubts. Thanks for the great info! I spent two days reading stuff online about this, but the posts on this forum were much better than anything else I read

So, is the P965 chipset memory bandwith of 12.8 GB/s simply to provide support for other processors (or perhaps to provide for future processors with faster clocks)?

Now just a dumb "marketing" question: Dell is selling new Conroe desktops and is advertising DDR2 667 memory even in their "value" systems. Does anyone know why they do this? If DDR 533 is all that they need, why do they spend the extra money to provide DDR 667? Is it simply because of their sourcing (i.e. they buy just one type of memory for all their systems), is it just marketing, or is there another reason? The fact that they do it on their cheapest systems suggests that the marginal performance increase is NOT the answer. Then again, trying to second guess Dell is probably a useless exercise :roll:

Sorry for all the questions. I am very new to the "industry" of building my own computer and overclocking, so I am as ignorant about most technical aspects as I am about how the industry works. I am trying to learn as much as I can so I can confidently put together my first system.

 

[lopri]

Yes that's partly for marketing and partly for practical reasons. As mentioned and shown by AnandTech reviews, faster memory can show (albeit small) performance advantages. On top of that I'm not sure how Dell configure their systems but if DDR2-667 is clocked at 266MHz (DDR2-533), that means more headroom - more stability.

I highly recommend this 2GB kit for people on budget. These sticks are reportedly using Micron D9 chips and reading the reviews make me believe that's indeed true.