What's up with Sandy Bridge only being rated for up to 1333mhz memory?

[Tig2575]

Can someone explain this to me? Why are sandy bridge processors only supposed to work with memory of up to 1333mhz (is that a specific limitation of the integrated memory controller?) And if it's only designed to work with memory of up to 1333mhz, then why then can I plug in two 1600mhz sticks and have the memory function perfectly fine?

Thanks all,
Tig

 

[jimmysmitty]

The CPU can still run the faster memory its just that Intel speced it to 1333MHz memory. When SB came out (last year) we were just getting 1600MHz memory into a good cost per GB.

Now you can get 8GB of great quality 1600MHz for $50 bucks but again that wasn't the case at the time.

Plus the benefits of faster memory are almost minute with desktops because most applications do not need the memory bandwidth, servers and VM machines however do.

Currently running SB with 1600MHz RAM is the sweet spot. Overall the performance is great and you get the great price. But its not needed as I said, you wont see any major benefit from it. Its much like 1866MHz or 2000MHz+ memory. Unless you are running a AMD APU, you wont benefit in performance from it at all.

 

[Tig2575]

Thanks, Jimmy! I just picked up a few components for a simple 2500k build for my brother to play Diablo 3 with earlier today, and actually did go with exactly what you said: 8gb of 1600MHz for almost $50 on the mark

Can you possibly go into more detail about what exactly you mean when you say Intel 'speced' it to 1333MHz memoy'? Is there some part of the microarchitecture that they had to fine tune to work best with 1333MHz?

 

[jimmysmitty]

As you stated earlier, the IMC is what is limited. Its mainly limted to 1.5v so as long as the memory is 1.5v it will run at whatever speed its rated. The Corsair Vengance is XMP so it will pick up 1600MHz in most mobos automatically.

But as I said, at the time 1333MHz was more comming, had better timings and was more cost effective. Right now its 1600MHz RAM and Ivy Bridge does 1600MHz as its best speed.

I am sure Haswel (the next CPU from Intel) will move to 1866MHz RAM or higher depending on whats common and easily affordable at the time.

For your brothers system, it will probably run great with 8GB of 1600MHz. I am personally waiting for Max Payne 3 that is recommending 16GB of RAM which I have. Kinda scares me that it wants so much.....

 

[mathew7]

And if it's only designed to work with memory of up to 1333mhz, then why then can I plug in two 1600mhz sticks and have the memory function perfectly fine?

One question: what is the frequency the BIOS configures?
Rating is the maximum guaranteed to work. A 1600MHz memory can work even at 1000MHz. It's just that it was tested an works up to 1600. But if it requires 1.6V or more for 1600, then it's actually an overclock-friendly 1333MHz memory. JEDEC does not allow >1.5V for DDR3.

 

[Tig2575]

^^ I don't have that info on-hand right now, as I'm out of town for a few days!

As you stated earlier, the IMC is what is limited. Its mainly limted to 1.5v so as long as the memory is 1.5v it will run at whatever speed its rated. The Corsair Vengance is XMP so it will pick up 1600MHz in most mobos automatically.

But as I said, at the time 1333MHz was more comming, had better timings and was more cost effective. Right now its 1600MHz RAM and Ivy Bridge does 1600MHz as its best speed.

I am sure Haswel (the next CPU from Intel) will move to 1866MHz RAM or higher depending on whats common and easily affordable at the time.

For your brothers system, it will probably run great with 8GB of 1600MHz. I am personally waiting for Max Payne 3 that is recommending 16GB of RAM which I have. Kinda scares me that it wants so much.....

Thank you, sir