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Author Topic: Observation of memory timings  (Read 5284 times)

janglur

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Observation of memory timings
« on: November 21, 2012, 08:32:08 pm »
Now that I got a new computer, I decided to put my old memory-timings theory to test.  My system has 1600 MHz DDR3 with CAS 11 (11-11-11-28-39-2T) latency.  (For the record, that's 13.75ns)

So I benched a fort.  I got an average of 66 FPS.  Okay.

Then I tried 1676 MHz CAS 11 (11-11-11-30-41-2T).  (That's 13.12ns)  FPS is now averaging 64 FPS.

Then tried 1522 MHz CAS 10 (10-10-10-27-37-2T).  (That's 13.14ns)  FPS is now averaging 72 FPS.

Next is 1370 MHz CAS 9 (9-9-9-24-33-2T).  (That's 13.13ns)  FPS is now at 78.

And then comes 1218 MHz CAS 8 (8-8-8-22-30-2T) (13.13ns)  FPS is now 81 FPS!

That's the entirety of the SPD chip defaults for my RAM.  So next, I underclock...



Then I set it to 800 MHz with CAS 6.  (6-6-6-15-20-1T) (That's 15ns).  FPS is now averaging 98 FPS.

Then I tightened it to 800 MHz with CAS 5 (5-5-6-15-20-2T) (That's 12.5ns).  This is technically an overclock since the response time is 12.5ns, which is less than the defaults of 13.12ns to 13.14ns the SPD chips provide, even though the frequency is much less.  FPS is now averaging 95 FPS.  This is as low as I can go with the frequency divider, and the tightest I can get timings and still be stable.  Also the chip's temperature dropped a whopping 9 degrees at both 800 MHz settings than it was at with all the others, which didn't change much.


Then I overclocked.  1830 MHz with CAS 13 (13-13-13-39-45-2T).  (That's 14.21ns)  FPS is at the worst yet, pushing only 44 FPS!


So, clearly, we can see that latency makes a huge difference to DF, while a higher bus speed and throughput is largely irrelevent.


I'd be interested if any other tech gurus can try the same and report the findings.
BTW, the formula to find your response time in nanoseconds is thus:
1000 / BUS * CAS   (Remember the BUS is double on DDR.  So PC-3200 for example is 400 MHz, which is effectively 200 MHz for this calculation.  To convert the 'PC-Rating' to MHz, just divide by 8.  So, in a nutshell, (PC-Rating/8)/2 = Frequency.  As long as you don't bring the frequency too high, watch the temp, and don't overclock by lowering the ns from the default(s), you should be alright, but of course, use at your own risk!)
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