Someone please help me with memory

[mchammer]

I'm sure many of us here remeber the old days of SDRAM when things were easy. There was PC66, then PC100, and finally PC133. Standard memory was 3-3-3 and the good stuff was 2-2-2. With Intel chipsets, the memory speed was the same as the FSB.

So today we have the P965 chipset and C2Ds with 1066FSB. So to me that would require DDR2-533. My question is that most of the advertised DDR2 I see is DDR2-800. Does this mean that today the FSB and memory bus don't run at the same speed anymore?

If I buy a P965 board and some DDR2-800 and leave all the settings alone what will everything be running at?

What if I do the same but with a P35 board and a 1333FSB C2D?

Thanks everyone.

 

[Rike]

Originally posted by: mchammer
So today we have the P965 chipset and C2Ds with 1066FSB. So to me that would require DDR2-533. My question is that most of the advertised DDR2 I see is DDR2-800. Does this mean that today the FSB and memory bus don't run at the same speed anymore?

Correct. With a 1066 FSB, you run DDR2-800 on a 2:3 ratio.

If I buy a P965 board and some DDR2-800 and leave all the settings alone what will everything be running at?

Most mobos should auto detect the speeds and set your ratio accordingly. However, I've noticed that RAM with tight timings typically need to be set manually in the BIOS. They'll boot fine with auto settings, but then you set the BIOS to the tighter timings.

What if I do the same but with a P35 board and a 1333FSB C2D?

Same as above but the ratio would be 5:6.

 

[mchammer]

So if I go out and buy a nice Dell or HP, the memory will run at DDR2-800? They just change the ratio as needed? I remeber in the old days, the ratios were always 1:1.

 

[Rike]

I can't attest to that personally since I haven't bought a prebuilt in about a decade. If you're concerned about it, you could always use a memory finder like the one on Crucial's website. That way you could check what type of ram you would be able to add to the specific brand and model before you buy it.

Prebuilt boxes are sometimes picky about the SPD timings and may not let you change to tighter timing if you have ram that otherwise would be able to do that.

 

[lopri]

I'd think Dell, HP, etc. will ship the systems with strictly to the specs. And they should list the specs in the product description. Say if you see a system equipped with an E6600 (1066 FSB = 266 x 4) and DDR2-800 (400 x 2), then it's pretty safe to assume that it's running 2:3. (266:400) If it says DDR2-667, then it's configured 1:1.

 

[JustaGeek]

With FSB = 266MHz and 667MHz memory, the memory divider is 10:8, or 5:4.

With FSB = 266MHz and 800MHz memory, the memory divider is 3:2.

I mentioned 10:8, because that's what Everest shows as a divider, or the DRAM/FSB ratio on the 775Dual-VSTA (my other motherboard).

I am running 325MHz FSB now, and 800MHz memory - my DRAM/FSB ratio is 16:13.

ASUS P5N-E SLI and NVidia 650i chipset allow me to run the FSB and the memory bus "unlinked", where BIOS will find the closest possible memory divider by itself. All I have to do is enter the FSB and the memory bus frequency in BIOS, e.g. 1300 (4x325) and 800.