Clock Rates of Mystery and Imagination

Aside from temperature issues, I found two oddities with new system that I can’t quite explain…

1. The Variable Video Card

The standard clock rates of an Nvidia 8800 GTS are supposed to be 500 MHz core and 800 MHz memory. But nTune shows 513 and 792 MHz for my eVGA model, respectively! Some googling tells me that these values are apparently common among reference designs. Not that it makes a huge difference, but… whence this discrepancy?

2. The Deceptive DIMM

I’m using two 1 GB memory sticks, type Kingston HyperX KHX6400D2LL/1G. These are advertised and labelled as DDR2-800 CL4 models. Imagine my surprise when I put them in my motherboard and see them auto-configured as DDR2-667 CL5! Checking with CPU-Z assures me that this is indeed their maximum built-in SPD configuration.

What’s going on? Did I get ripped off? No, as the PDF data sheet on the Kingston website shows, these are in fact 800/CL4 models that deliberately misconfigure themselves as 667/CL5!

The reason is apparently that they require 2.0V in 800 MHz mode which differs from the standard voltage of 1.8V. Once I turned off SPD auto-config and manually entered the clock rate and access speeds they worked just fine (as per Memtest) in 800/CL4 mode.

But why doesn’t SPD specify the required voltage, too? Or why doesn’t the memory maker leave that up to the motherboard? This nonsense basically invalidates the whole idea of SPD configuration – the motherboard might as well choose its own safe values if the SPD values are so much lower than what the memory stick can actually do.

Dunno about the video card, but I think the JEDEC standard for DDR2 voltage is 1.8v, so memory makers can’t sell stuff where the SPD is set to something higher. That’s why Nvidia/Corsair came up with the whole enhanced performance profile memory, but the BIOS needs to recognize it. EPP memory will default to standard SPD in a non EPP-aware BIOS, but in an EPP-aware BIOS, you can select a single profile, and the BIOS will be set to the correct voltages, timings, etc.

Interesting. Sounds like a really shortsighted decision to define a single voltage that all SPD configs have to conform to. I’ll have to check whether my Asus mobo would recognize this Corsair EPP stuff but I don’t recall seeing it in the manual.