What RAM frequency for a 1333 mhz FSB?

[blyndy]

Hi,

I'm planning to build a new system. I sought out that sticky (this one) that describes the relationship between FSB/DDR.

I was happy that the e8400 was the example 'coz that's what I'm getting:

Let's take an E8400 Wolfdale dual-core, shall we? It has:
a multiplier of 9x
a FSB of 1333mhz
a speed of 3ghz.

Now, 1333x9 is 12ghz, which is definitely not the speed of your CPU (sorry)
To get the actually speed of the chip, divide the FSB by four.
1333mhz/4 = 333mhz.

Now, let's try again:
9x333=3.0ghz (2997mhz if you're picky)

So you need to use DDR2-667 RAM with this CPU at least. (667/2 = 333)

This is a useful chart explaining what FSB and memory work well together

Unfortunately the url to the chart has turned into an ad-farm and The Internet Archive doesn't have a backup. Anyone know a similar link?


Anyway, I'm still unsure on a few things.

1. If I turn on a FSB/RAM ratio of 1:1 will the RAM be automatically downclocked to 333mhz?
2. If I turn off the 1:1 ratio and stick some 533mhz 4-4-4 sticks in will the performance go up significantly?
3. Is the price difference between 333mhz 4-4-4 and 533mhz 4-4-4 DDR2 significant? would it be worth the added performance if any?
4. It says that the FSB needs at least 333mhz DDR2. I infer that anything less would starve the CPU. How does the CPU benefit from a higher RAM frequency anyway?

 

[Spoelie]

1. yes
2. performance will go up but not significantly
3. even if you would find 533mhz 4-4-4 it would be extremely expensive and not worth it. 533mhz 5-5-5 is what most people buy. In practice you should go for at least 400mhz 4-4-4 and step up to PC1066 if the price difference is minimal (so depends on where you buy).
4. http://forums.anandtech.com/me...304189&highlight_key=y (second post & lower)

 

[PlasmaBomb]

DDR2 667 is still pretty cheap -
First hit on newegg-

$27.99 for 2GB, PC2-5300, timings 4-4-4-12.

There should be an option in the BIOS to run it at 2x the FSB (Ratio 1:2, FSB:MEM)

In fact there is DDR2-800 (PC2-6400) at $24.99 on the egg too (Cas 6, 1.8V).

The DDR2 1066 (PC2-8500) starts from $15.49 a stick (1GB)

Cheapest Dual Kit 2x 1GB is $30.99 (Cas 5, 2.1-2.3 V required)

That should let you run > 400 FSB (3.6GHz +) at 1:2 divider.

The DDR2 1066 seems like the pick of the bunch for an extra $6. Feel free to shop around, I am not from the US so you may find better prices.