CAS Latency & RAM

[slipknot.giorgos]

I just got a new ram. Specifically the 16GB Corsair Vengeance LP 2x8GB (cml16gx3m2a1600c9)
Default says 1600MHZ at 9-9-9-24 cas latency. I did some experimenting and my PC couldnt boot many times until I randomly found on this site an article and tried 1866mhz at 10-10-9-24. I have 2 questions. 1) Since it was made to be by default at 1600mhz at 9-9-9-24 why was it automatically at 1333mhz? Is this something caused by my power supply?
2)How can I know or find which cas latency is the right one? Like I said in order to use in 1866mhz I upgraded Voltage at 1.65 from 1.5 and changed the cas latency.

 

[Barty1884]

1. 1333MHz is the DDR3 JEDEC standard that all (modernish) DDR3 runs at "out of the box". 1600MHz is what it's rated for, but that's technically an OC, achieved by enabling XMP on compatible motherboards. It's essentially a saved OC profile for those dims.

2. The 'right' CAS latency, is the lowest that'll work to provide you with the required speeds. The 'stock' CAS for the 1600MHz speed was 9. You've bumped to 10 for 1866MHz. At a very simplistic level, you want the highest clock speeds.... paired with the tightest timings (including lowest possible CAS).

 

[slipknot.giorgos]

Do you think (from ur own experience) that my timings are correct? Plus i have and amd fx 4100, isnt XMP only for intel? Even if its not, can i access it in my bios to get the right configuration for 1866 OC?

 

[zyh1987]

since you are working off an amd chip, likely you will have these issue as xmp is a intel spec. The memory controller for amd and intel are different. Same timing may work on one but no the other. There is no way to *make* a chip for a specific timing, common practices are binning, which puts a chip under a series of test and category them by tests. However there are two parameters when buying ram, grew and cl timing, some chip can make both bins and are usually made into the product that sells more. As far as test goes, run mem test and other mem torture test, as long as they pass. You are good to go.

 

[Barty1884]

You've barely loosened anything, really. Provided it's stable (I assume you've run MemTest?), then yes, they'd be "correct".

XMP *technically* is for Intel only.... but, plenty board vendors include a variant for AMD - "A-XMP" and similar names have been used.
Regardless, manually setting the timings of the "XMP" profile typically work for AMD too, just not guaranteed.