XPS 420: RAM Frequency is 667 MHz instead of 800 MHz.

The most logical thing is that the new memory is mislabled and is 667 instead of 800.  The Memory will run at the speed of the slowest memory installed.

Well mixing the latencies can definitely have an effect, in that the  memory controller will try to run all the ram according to the SPD's that are programed into the sticks. Since 6 is slower that 5  the controller will try to run the CL 6 at the CL 5 timings, and most likely there is no CL5 timing programed in the CL 6 sticks, then the memory  will fall back to the slowest ram timings in order to prevent the memory controller from self destruction.  The most easy way for it to do this is to lower the speed.

You best bet is to have all the ram the same.

I am pretty much sure that the two new RAM modules run at 800 MHz by default, since I have checked the code number of these modules. The only difference is the latency itself. I believe that by logic, all my 4 RAM modules should be able to run at 800 MHz, albeit at larger latency of the new RAM. However, such is not the case. Well, since the CL5 RAM is not available near my place, I was forced to purchase the CL6 RAM. Still, I am sure that the CL6 RAM can run at 800 MHz.

Another theory worth speculating is regarding the XPS 420 motherboard. As compared to using just 2 RAM modules, using all 4 RAM modules may decrease the motherboard stability and increase power consumption. To maintain stability, the motherboard will decrease the RAM speed.

If such theory applies to the XPS 420 motherboard, I will be utterly disappointed. I checked the User manual with no indication that RAM speed may be reduced when all RAM slots are used. I paid premium price for XPS 420 (at that time, Alienware was not offered by Dell then), and you are telling me that  the XPS 420 motherboard cannot use all 4 RAM modules without decreasing RAM speed? Come on, Extreme Performance Desktop (XPS) would have meant something, right?

Sorry for harsh tone here. It is just that i am expecting top-notch performance from my XPS 420 desktop. Any advice is very much appreciated. Thank you.

I am pretty much sure that the two new RAM modules run at 800MHz by default, since I have checked the code number of these modules.
* Pull the original Dell memory and leave the new 2GB in there. Run CPU-Z. What is the MHz? They must be PC2-6400. If they are PC2-5300 they are 667MHz.

The CPU-Z report file generated when it only has the original 4 GB RAM:

The CPU-Z report file generated when it has all the 8 GB RAM:

The following is the proof that the 2 new RAM are of 800 MHz type:

The last image states that my RAM modules are running at  667 MHz, although they are all of 800 MHz type:

Please provide some guidance to me, so that I can tweak the RAM to run at 800 MHz. Thank you very much.

Can anyone help me please?

I'm very curious what you ended up doing with your XPS 420 . . .  I'm just now discovering this problem. I was orignally running:

STOCK - 2 x 1GB PC6400 800mhz  

STOCK - 2 x 512MB PC6400 800mhz

This gave me 3GB at 800mhz verified in BIOS, but when I went to drop in G.Skill 2 x 2GB PC6400 800mhz with a Latency of 5,  along with the STOCK - 2 x 1GB PC6400 800mhz I was shocked to see 667mhz in my BIOS settings. Sounds like the SAME ISSUE. Unfortunetly this maybe my last Dell as it should be everyone else in this post, they made their last excuse. I spent and hour with an XPS tech trying to explain this to him. He only proceeded to tell me though its not impossible in most likely improbable and that was that. This motherboards eSata port also gave me hell, though they fixed the issue, it is by far perfect as it takes twice as long to boot the controller.

Did you ever purchase the secound identical RAM set, and if so, did it work? I really don't want to buy $65 of 800mhz RAM if I'm only going to get 667mhz out of the XPS motherboard.

Thanks!

Your problem is mismatched ram. Even though the specs might appear the same any slight difference in the ram sticks will cause the ram to run at the default speed.

So your saying you can't just match the RAM's MHZ as I have (PC6400 - 800MHZ). I also have to match other specs such as Latency, power or other wise? These are different sets of RAM, yes, but they are also utilizing different channels. Both sets of RAM are 800 MHZ by default. I have never heard this in any forum or other wise, might you elaberate what you mean by mismatched.

Either way if your saying they are mismatched, I should be able to purchase another set of fancy G.Skill RAM and I'll reach 800MHZ. Instead of pairing my set of cheap 800mhz DELL RAM with a better set of 800mhz G.Skill RAM.

Don't forget the other guy in this forum was also running a XPS 420 motherboard, this couldn't be the issue?

Yes there are other things in the sticks besides the speed and voltage. Each stick has its own little program call a SPDT. this is what the memory controller access. That is the main reason you should always upgrade your ram all at a time.

Even if you purchase one set now and then another set later on even if the sticks are the same model number they could have a different SPDT program in them.

I have been there. when i upped my current ram from four to eight I bought two more 2x2 gig sticks of the same memory, but in the time between the vendor (OCZ) had modified the SPDT program. I had to have them provide me with a flash SPDT that i could flash onto all four sticks to make them identical. Then and only then did my memory meet stated timing specs but also they all ran at 800mHz vice 667

Davet50

Thanks for your explaination. Yes, all my RAM are of Kingston, with the same model number. The difference is that the first set of 2 x 2 GB RAM is of CL5, while the newer set is of CL6. Probably, the one year elapsed between the 2 purchases has caused the second set of RAM to have different SPDT.

So, how can I request flash SPDT from Kingston? Which flash SPDT should I use? The one from older CL5 RAM, or the one from newer CL6 RAM? Is there any risk in flashing the SPDT of the RAM, similar to the one for BIOS flashing?

Thanks for your information.

Not necessarily, I just bought 8gb of 800Mhz ram for my XPS , 4x 2gb all the same speed/brand/model/latency etc. The bios detected it all but it shows up as 667Mhz. That's how I found this thread, I was wondering what the issue was.

What does CPUID say? Click  on the memory tab and double the frequency reading.