12-21-2013 06:09 AM
12-21-2013 07:49 AM - edited 12-21-2013 07:50 AM
I did some testing earlier this year and did a short write-up and decided that the advantages of dual-channel, frequency and cas latency were more theoretical than practical. I was using a laptop with 2 slots, so it isn't quite the same, but it was an i7 Ivy Bridge CPU, so there should be more similarities than differences. This is what I wrote:
Probably more often than once a week, I see or hear a question regarding advantages of buying faster memory or using matched pairs of DIMMs. Obviously, using memory that is rated faster than the bus speed yields no improvement, and I always believed that advantages of "matched pairs" was more theoretical than actual. For no good reason, I decided to run a semi-scientific test. I have a T430s machine here, which will run at DDR3-1600 or DDR3-1333 mHz, depending on the memory installed. I also have 2 matched pairs of 8GB DIMMs. One pair is Corsair Value memory (DDR3-1333 CL-9) and the other pair is Corsair Vengeance, their "better" memory (DDR3-1600 CL-10). My idea was to test the memory 3 ways: 2 faster DIMMs, 2 slower DIMMs and mixing one of each type. My expectation was that the fast memory would run at 1600 bus dual-channel; the slow memory would run at 1333 bus speed dual-channel, and the mixed configuration would run at 1333 bus speed, but not use dual channel operation and be the slowest. First, I ran the windows7 "windows experience test". The faster memory gave a "memory operations per second" score of 7.6, while the slower memory gave a score of 7.5. The mixed option was the same as the slower memory.
I then ran Memtest86+. (the free memory tester I use) First, it became obvious why the mixed set ran as fast as the matched pair of slower memory. The mixed set was using dual-channel operation. I now assume that "matched pair" really means any 2 of the same size. When I ran the full memory test, the faster memory took 1:20:45. The slower memory took 1:21:55. I ran one more test to look at single-channel vs dual-channel operation. I ran just one of the faster DIMMs. If it were running at the same speed, the test would have taken half the time taken by the pair, or 40:23. It actually took 41:52, and the windows experience score fell from 7.6 to 7.2. I was going to complete the test by running 2 4GB DIMMs, but the only PC3-1600 4GB DIMMs I had were the ones that Lenovo includes with systems, and it is slightly slower that the DDR3-1600 memory I used (CL-11 VS. CL10).
It seems clear to me that one would never be able to notice any difference in any real application, but there was a measurable difference that would allow someone to win a "mine is bigger than yours" contest
12-21-2013 08:25 AM
12-26-2013 07:44 PM - edited 12-26-2013 08:09 PM
I have a WEI of 7,9 in memory (the disk is an HDD of 5,9 so overall is a 5,9) using 4x8 Gskill cl10 1600.
Dual channel means the processor will write to 2 dimms at once, that is, the word size will be double (half of what is written goes to one dimm the other half to the other) thus you will be using less time writing into the memory. As everything, you need the sw to take advantage of it. So it's better you make it work as that's the configuration you can have.
As far as I know, in older models you had to pick your slots (something like 1 and 3 (under the keyboard; 2 and 4 (under the laptop)) to make it work. obvioulsy you have to use same type of memory in both slots (same size, frequency, cl, cas,etc), get rid of the original dimm that the laptop comes shipped with (usually a 4GB).
For instance if you left your original sodimm module inside, and put two 8GB sticks in slots 3 and 4 you'll end up with a single channel configuration. In older models (prior w530) you had to open the laptop (removing the keyboard (it is demonstrated in the user's guide)), remove the original stick (the 4gb one), put the 8gb in slot 1, and put the other in slot 3 (under the laptop (the easy access memory upgrade slots)). Supposedley staring with the w530 you can put the both of them in slots 1 and 2 and have them working in dual channel mode but if that hasn't worked out for you, then use the slots that are paired as told.
Please don't buy into the "wrongly configured is the same thing" kind of motto. This is a very well known problem in the forum and one for which a solution is already known as posted here and in a lot of other posts. Just get the things right so when you use a sw that requires performance, like one for which a machine like the w530 has been designed for, those tiny microseconds actually begin to mean minutes or even hours of advantage. (on extensive simulations or renders)