What is the correct DDR2 memory speed for use with 1333 FSB CPUs?

[E-66]

This link on Wikipedia says Core 2 technology benefits from RAM running synchronously with the FSB. In their example they're using a FSB speed of 1066 as a reference and they say using DDR2 PC2-4200/533 or PC2-8500/1066 memory is best, which makes sense according to the charts. They go on to say that using PC2-5300/667 can actually decrease performance. Then they say that using PC2-6400/800 will provide a significant performance increase.... but PC2-6400 isn't running synchronously with the FSB. So why the performance increase, just because it's faster memory?

http://en.wikipedia.org/wiki/Intel_Core_2#..._memory_modules

Here's what I'm getting at... I want to do a new build with either a Conroe or Wolfdale CPU with a 1333 FSB. According to the chart on that wiki page I should use PC2-5300/667 in order to run synchronously with the FSB. When reading reviews of these CPUs on NewEgg I've noticed that a lot of people list their system specs. I have yet to see any who list PC2-5300/667 memory, they're all using PC2-6400/800.

Why? There's no cost difference. Is it because they had this memory left over from a previous build that used a CPU with an 800 FSB, or is the PC2-6400/800 a better choice than the PC2-5300/667?

Thanks.

Edited March 16, 2008 by E-66

[Kelsenellenelvian]

It really depends on your motherboard also.

[jcarle]

Memory speeds are usually best at 1:1 ratios (1333FSB means 667MHz memory), the next best thing is 1:2 with the CPU (1333FSB at 1:2FSB would be 1333MHz memory).

What a lot of people do, myself included is buy memory that's rated for higher then the 1:1 ratio would recommend, lock it at 1:1 and then overclock the FSB.

So if your FSB is at 333Mhz (1333MHz CPU and 667MHz memory) overclocking it to 400MHz would bring your cpu to a 1600MHz FSB and your memory (using 1:1) to 800MHz. So if you were using 667MHz memory to start with, you'd be overclocking your memory as well as your CPU (and it's a hell of a lot harder to overclock memory then it is a CPU), yet if you were using 800MHz memory to start with, even with the FSB overclocked your memory would simply be running at it's stock speed and only your CPU would be overclocked.

[E-66]

Thanks. So the reason they're using 800MHz memory is because they planned on overclocking? I've read that these CPUs are really easy to overclock. Haven't done much of it myself in the past but it certainly seems like something worth considering.

[E-66]

A couple followup questions....

1. If I want to overclock the FSB to 400MHz, does it matter which stock FSB speed the motherboard supports, or can that be adjusted in the BIOS? I'm looking at socket 775 boards on Newegg right now and see ones that support 1333(O.C)/1066/800/533, 1333(O.C.)/1066MHz, 1333/1066, 1066(O.C.)/800/533 MHz, and 1066/800MHz.

2. According to what you said above, if I'm going to overclock the FSB to 400MHz then I want to use DDR2-800 memory to keep it running synchronously with the FSB (I'mnot considering DDR3 due to price). So along the same lines as in the first question, does it matter what memory standard the motherboard supports, or do I definitely want to get one that only supports DDR2-800?

Thanks.

[Zxian]

Chances are people simply buy DDR2-800 because they don't know any better. They think somewhat blindly that faster RAM will give them better performance.

Overclocking is a bit of an art, and can be risky. Remember - you're pushing your hardware beyond it's designed limits, so there might be a point where it doesn't work anymore, or you might break something. The less you push a component past its rated settings, the less risk (in general).

[E-66]

I'm not planning on pushing everything to its limit. It's just that these CPUs seem to have so much margin for error for bumping things up a bit that I figured I'd try to get a little extra out of it, but I want to make sure I get the right memory and motherboard to start with.

[Zxian]

P35 chipsets seem to have a lot of headroom when it comes to overclocking. I'd recommend the Asus P5K series, or the Gigabyte EP35 and GA-P35 series. Personally, I'd go with a motherboard that has the ICH9R chipset (It supports RAID) for the added flexibility of setting up RAID arrays (only use RAID0 or RAID1 with the onboard though...).

In your case, by grabbing a Wolfdale CPU and overclocking it, you'll be pushing the motherboard and the CPU. If you run into a wall when overclocking, you'll have to figure out which component is holding you back. That being said, I've heard of people using the E8400 easily hitting 4Ghz without any second thoughts.

[puntoMX]

Memory speeds are usually best at 1:1 ratios (1333FSB means 667MHz memory), the next best thing is 1:2 with the CPU (1333FSB at 1:2FSB would be 1333MHz memory).

Chances are people simply buy DDR2-800 because they don't know any better. They think somewhat blindly that faster RAM will give them better performance.

That depends, I sell basically 800MHz as more computers go out with onboard VGA and there you will have a big performance gain.

EDIT: By the way, onboard VGA will be faster at 800MHz RAM setting, also throughput benefits a bit over 1:1 setting, as long as the timings don’t go worse...

[E-66]

I'm glad you mentioned that, Punto, because ideally I'd like to get a motherboard with onboard video. There are A LOT more Intel based motherboards on Newegg than there are for AMD processors, almost 3x as many.

The Wolfdale E8400 was showing as being in stock again just now so I ordered one. I don't know if I'll get one or not though. I tried it last week and before I even finished checkout I got a message that it had been removed from my shopping cart due to insufficient quantities. I made it all the way to Step 1 this time, guess I'll just have to see what happens.

[E-66]

What a lot of people do, myself included is buy memory that's rated for higher then the 1:1 ratio would recommend, lock it at 1:1 and then overclock the FSB.

Could you (or someone) explain the 'locking' part in more detail? The motherboards I've had up until now haven't had a whole lot of overclocking options in the BIOS, is this just some setting I've never seen before?

I'd like to do exactly what you mentioned in your post above - use DDR2-800 memory and overclock the FSB from 333 to 400MHz. That will keep the memory running synchronously with the FSB, won't overclock the memory, and take the E8400 from 3.0GHz to 3.6GHz.

According to what in an article on Tom's Hardware specifically about overclocking the E8xxx everything should remain stable since this is pretty conservative overclocking, at least as far as this CPU goes.

Edited April 11, 2008 by E-66

[E-66]

I don't want to go too far off topic, but what's the deal with the oddball memory speeds I've seen on Newegg like these?

DDR2 675 / PC2 5400

DDR2 900 / PC2 7200

DDR2 1000 / PC2 8000

DDR2 1100 / PC2 8800

DDR2 1111 / PC2 8888

DDR2 1142 / PC2 9136

DDR2 1150 / PC2 9200

DDR2 1173 / PC2 9384

DDR2 1200 / PC2 9600

DDR2 1250 / PC2 10000

DDR2 1300 / PC2 10400

[jcarle]

E-66 asked me the following and I thought my reply could be useful in this thread:

You mentioned getting memory that's rated for higher than the stock 1:1 ratio, locking it at that speed, and then overclocking the FSB to match it at the new faster 1:1 ratio. I understand the concept of what you're saying, but I don't understand how the 'locking' part is done. Is it determined by whether or not the motherboard has BIOS settings that allow it to be done, or something else?

Depends on the motherboard you have. Some have a setting dedicated to establishing the ratio between the FSB and the memory, you'll see options like 1:1 2:1 1:2 5:4 3:4, etc... however most modern motherboards, especially ASUS ones, have memory speed settings instead. First you need to determine your motherboard clock speed based on your FSB. Knowing that Intel processors have quad pumped FSBs, your true clock speed is divided by four. So if your CPU is running a 800FSB processor, your clock speed (800 / 4) is 200. DDR memory is double pumped at 1:1, so to get 1:1 with a 200 clock, you need to run your memory at 400MHz. What happens then when you overclock, your memory will follow and still be within the specification it was designed for.

So say you overclock your motherboard's FSB from 200 to 333, which a lot of motherboard easily support due to new processors originating with 1333FSB, you memory if still at 1:1 will now indicate that it's running at 667MHz. If you were to push the FSB to 400MHz, your memory would now be running at 800MHz, as it was originally. However, now instead of running at 1:2, it's running at 1:1. The cpu is now running at double it's speed, the FSB and interconnects are at double speed and the memory is still running at stock speeds. (Memory is the touchiest thing to overclock).

[E-66]

In my case it's a Wolfdale E8400 with a 1333 FSB, so that makes its true clock speed 333MHz. As I mentioned in in one of my posts above, I want to overclock the FSB to 400MHz to match the DDR2-800 memory. I haven't made any BIOS changes yet, but I think I recall seeing 5:4 when I was looking through the BIOS settings earlier. Hopefully the settings allow me to make the necessary changes.