Memory rated at 2-3-3-6, but Bios shows 2.5-4-4-8. Mobo=Intel D915GAG. Is speed diff a problem?


I've purchased a pair of PQI DDR400 memory sticks, rated at 2-3-3-6.  This memory was selected because it was faster than most other memory, and still in the reasonable price range.

After installing the memory sticks, the Bios shows the memory as being 2.5-4-4-8.  

In the Bios, under Advanced -> ChipSet Configuration -> Memory, there are some memory adjustments that can be made.  
SDRAM Timing Control = Manual [Auto, Manual-Aggressive]
CPC Override = Enabled [Disabled]
SDRAM frequence = 400Mhz [266, 333, 533, 667]
SDRAM tCL = 2.0 [1.5, 2.5, 3.0]
tRCD = 3 [2, 4, 5]
SDRAM tCP = 3 [2, 4, 5]
SDRAM tRASmin = 6 [3, 4, 5, 7, 8, 9, 10,11,12,13,14,15]

Total Memory = 512MB
Memory Mode = Dual Channel
Memory Channel A
  Slot 0: 256 MB SPD: 2.5-4-4-8
  Slot 1: not installed
Memory Channel B
  Slot 0: 256 MB SPD:

Note: SPD defined as tCL-tRCD-tRP-tRASmin

I'm interested that, even though I've explicitely defined the memory speeds, the mobo seems to have evaluated the memory timings and overrode my settings.  If the memory would not be stable at a faster speed, I can appreciate a safety override.  However, I bought what I thought was faster memory.

My questions:

Is the memory actually slower, or am I giving the mobo too much credit for intelligence and not expressing the memory speed correctly?

Is this speed difference practically measureble, and a significant and noticeable difference in application amd computational performance that I should be concerned?

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Steve McCarthy, MCSE, MCSA, MCP x8, Network+, i-Net+, A+, CIWA, CCNA, FDLE FCIC, HIPAA Security OfficerIT Consultant, Network Engineer, Windows Network Administrator, VMware AdministratorCommented:
I would set your motherboard settings to Auto or By Speed as the bios is looking at the memory and taking into account the latancy in your system.  I did the same with Kingston HyperX memory and a bunch of others in an ASUS motherboard I was having problems with.  It seems that when I tried to adjust for exactly what the memory was rated at, it went slower, but if I let the system detect and set what it liked, everything seemed to run optimally.  RAM in different motherboards can perform differently depending on the Bios, chipset and manufacturer.  Some are better and more efficient than others.  I can tell you from experience that I could not tell a difference in performance between Kingston HyperX with a Latancy of 2 and the Value Ram or Viking with a Latancy of 3.
A mobo usually doen't override manual settings. From experience I know memory can be overclocked .5-1 ns (cas settings) or 50-100Mhz (fsb/mem settings). Some mobo's do override settings, while others just refuse to boot (you'll need to rest bios by jumper then). I this you'll need to disable the 'cpc override', as it's the most likely culprit.

Blue Rishi

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