1333mhz RAM on a 1066mhz CPU

So if my CPU maxes out to 1066mhz ram compatibility I Assume the ram will just clock itself down to 1066.

But what about things like the Cas latency? Will that remain the same? I just want to know what exactly will be affected by clocking it down from 1333mhz to 1066.

edit: Essentailly, would I benefit at all from buying 1333mhz over 1066mhz.

 

I think it will be lower.

Also there are a few 1066mhz fsb laptops that do support 1333mhz RAM.

 

How do I find out if mine does? Doesn't the processor determine it?

 

No not always.
There are lots of laptops that support the best Core 2 series which have 1066mhz FSB but they still use ddr2 800mhz RAM.

My laptop says it supports 1333mhz but I haven't been able to tell for sure, there are a few different pieces of software that will report the RAM speed you are actually running and they give some conflicting results.

 

Yep, the ram will just clock down down to 1066MHz. I think CPU-Z can check your memory speed.

 

The Latitude 13 comes with an 800MHz FSB processor (ULV) and it ships with 1333MHz DDR3.

 

Just buy the 1333Mhz ram. The price difference is nil and the drawbacks are none.

I'm not saying it doesn't, but that doesn't necessarily mean it uses DDR3-1333 though.

 

It all depends on the programmed timings (SPD).

Usually you find that higher speed modules dont bother with proper lower level speed timing programming.

I like my ULL 1066mhz kit.

5-5-5-15 which also lets me run some other important sub timings lower.

 

I used to play the ram timing game with my old socket A system, but these days I feel that it is just a waste of time. What do you use to manipulate ram timings in software?

 

I believe Thaiphoon burner is the standard for ddr3, spdtool is pretty dangerous.

There is an older trial version which will flash the modules unlike the newest trial versions.

What I don't understand is how to perfect your timings for your laptop. I think the m860tu doesn't run well with strange timings... at least, I'm very unsuccessful with trying to stabilize 1333mhz FSB...
Even with 1333mhz RAM and overvolted CPU...

Do CAS latencies really get lower when RAM gets downlclocked?

 

Latencies should be lowered. You can check out the timing tables to be sure. It would be the SPD tab in CPU-Z.

 

Yeah but it will not be as good as a propper slower kit.

There is a chance you will end up with 1066mhz 9-9-9-21 ram.

I use a memset to change the latencies every boot.

 

I guess I should just stick with 1066, I'd rather not screw anything up =p

 

Up to recently CPU's have had virtually nothing to do with the amount (and type) of RAM you can install in a laptop except for how much memory they can address. Nowadays more and more laptop CPU's have the memory controller integrated onto the same package as the CPU (often same die) so this changes how you find an answer.

In either case, whether the memory controller is within the northbridge or within the CPU then it's what actually determines what memory you can install, how much of it, and what speed grade (frequency) is supported.

SODIMM memory is backward compatible, this has been the case since SDRAM where PC133 SDRAM would work in a PC100 SDRAM compliant laptop, PC2700/3200 DDR in a PC2100 DDR compliant laptop and so forth.

You can virtually always install a faster speed grade SODIMM and such configuration will work, the worst that can happen (and happens at times depending on your model of laptop thus memory controller) is that the faster SODIMM will work at the frequency of a slower speed grade (i.e. PC2-6400 DDR2 might still only work at 667MHz thus a PC2-5300 speed grade).

In rare cases some laptop manufacturers block the BIOS so the memory can't run faster even if the memory controller supports a faster speed grade (i.e. say PC2100 DDR but the BIOS is locked to PC1600 DDR - such as was the case in the early Sony GRX series for example, back in 2002).

Even if your laptop doesn't support running PC3-10600 DDR3 at its rated speed of 1333MHz it will in 99% of cases just downclock it and run it at PC3-8500 thus 1066MHz speed. This configuration is stored in the SPD of the PC3-10600 regardless. Your laptop's BIOS will read the SPD data, determine a valid configuration and set all the installed RAM at the slowest denominator supported by all the installed SODIMM modules.

In short, don't fret about it but go with what you currently have installed as the chances your memory controller supports a higher speed grade (magically running at 1333MHz) are probably non-existent. Yes, laptop manufacturers to cut corners with RAM to improve margins but they usually don't install slower RAM than what is supported by the memory controller.

 

hmm interesting.

Are there any tools to read BIOS and ACPI and get info on how exactly the downclocking occurs?

I think I actually had a laptop not start on me recently with 1333mhz RAM in it. Not sure but I'll check. It was also with a 667mhz FSB CPU I dont know if that has anything to do with it.

 

In other news... I'm trying to figure out what this means...

 

it,s runing a 800 mhz with 6-6-6-15 cas

 

What about the one thats originally 1333mhz?

 

You have mixed 800mhz ram with 1370mhz ram and both are now running @800mhz.

What are you trying to figure out?

 

All ram in the same computer will run at the same voltage, timings, and frequency.

 

Well I'm trying to figure out if there is anything glaringly obvious that my m860tu acpi or bios is doing with my ram timings to affect stability in a major way while eventually overclocking to 1333mhz FSB.

Doesn't it look a little more like one module is running at 457 and one at 466?

I dunno, I guess I'm just trying to understand definitively why 1333mhz is unstable and if it has to do with my RAM or not, because it seems like when I try to flash it to 400 instead of 533 but actually keep the latency from 533 my m860tu just ignores it or something.

 

The timings and latencys for each card are different at each FSB so I think that may be ur stability problem

 

I only have the other module in there right now to see what it does... It isnt any more stable when I take the 1333 module out.

 

I would take out the 800mhz ram.

Then check at what frequency the 1333mhz ram runs at (with CPUz).

Then when you know that frequency (for example imagine it was 1066mhz (533mhz real)), change the timings of that frequency to the highest timings in the table (9-9-9-25).

So the 1333mhz ram would be running @1066mhz with 1333mhz timings.
That should give you some overclocking headroom.
With that setup you would be able to get the FSB to 1333mhz while having the ram run at what it was rated for (1333mhz with 1333mhz timings).

If you wanted even more headroom, flash the 1333mhz ram to 900mhz and keep the 1333mhz timings.