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2x2GB + 2x4GB - Does dual channel works?

Last response: in Memory
March 29, 2011 10:03:05 AM

Hi. I wanted to upgrade my laptop memory so I went out and bought a 2x4GB set to replace the existing 2x2GB modules.
I didn't do the proper research before I bought the modules, so now I'm in trouble...

The thing is: I found out that the motherboard houses 4 slots. The existing 2 slots are not accessible where one normally replaces ram. Instead it is placed out of immediate reach somewhere on the motherboard. I therefore installed the new ram in the 2 empty slots resulting in 12gb ram total.
This is further complicated by the fact that the existing ram run at
DDR3-1333, cas 9
and the new ram run at
DD3-1066, cas 7

CPU-Z tells me this:
Existing ram x 2 -->

New ram x 2 -->

Other laptop info -->

1. Is is possible that the system can handle dual channel on both sets? - or does the entire thing run in single channel? CPU-Z tells me that it is DUAL-channel but I'm not sure if I should trust it.
2. I reckon the all the ram now runs at the speed the new ram dictates which is 1066MHZ at cas 7? Does this affect the speed of the CPU or can it figure out that it should apply the correct divider? It seems that the system changes the multiplier dynamically according to CPU-Z. I guess this is related to Turboboost-tech?

More about : 2x2gb 2x4gb dual channel works

a c 128 } Memory
March 29, 2011 10:36:26 AM

Oem boards by dell, hp, packard bell, etc. don't work well with different sets of ram; best to match the original set to guarantee it will work. Your board may also have a limit of 2 gb per ram slot. You'll just have to try the new set of ram; if it doesn't work and you can't return it, try selling it in anandtech's hardware forum or craigslist.
a b } Memory
March 29, 2011 11:45:40 AM

If CPU-Z is telling you that it is running in dual channel mode, it is.
Related resources
March 29, 2011 1:12:03 PM

Thanks for the replies.

o1die: The ram is installed an confirmed to work. This is the data from CPU-Z

jsc: OK, I guess so.

Do you think it will have any performance penalties to run the dual channel of different amount of memory?
a c 128 } Memory
March 29, 2011 9:18:31 PM

Nope. Run it. Your board has few if any ram adjustments. You're lucky it works at all.
a c 347 } Memory
March 29, 2011 9:40:26 PM

^@o1die - Congrats on the Gold! :) 

Looking at the 'Mix':
1066 7-7-7-20 @ 1.5v JEDEC #2 {Samsung}
1066 7-7-7-20 @ 1.5v JEDEC #2 {Corsair}
1066 7-7-7-20 @ 1.5v Mix

The 'Problem' would be to get them to run at Rated Frequency.

1333 MHz Samsung
1066 MHz Corsair

ANS 1 - As long as you run them at 1066 7-7-7-20 @ 1.5v it should be fine, and as stated CPU-Z is showing 'Dual.'

ANS2 - No, the i7 720QM IMC is DDR3-1066/1333 -- the only limitation is the 1066 MHz won't saturate the IMC's 21 GB/s limit. The difference between 1066 and 1333 {CAS to CAS} is 1~3%. So on a Laptop this is impossible for you to notice, a benchmark yeah maybe -- depend on the RAM IC.

Whatever you've got and it works then leave it alone!

However, to be on the safe side run Memtest 86+ 2~4 passes; make a bootble CD/DVD {ISO/zip}

Good Luck!
March 30, 2011 8:07:03 AM

Thanks guys.
Ran a mem-test via the bios utility which gave me a OK.
Have been running the setup now for a day, and so far no stability issues experienced.

I'l take the advice with the memtest, but currently do not have time to go through it, because I'm running a project with a tight schedule. Will look into later.
a b } Memory
March 30, 2011 8:37:24 AM

I have had different memory sets run in Dual Channel mode.

Channel 1
Slot 1: 4Gb
Slot 3: 2Gb

Channel 2
Slot 2: 4Gb
Slot 4: 2Gb

or whatever slots arrange in whatever channel.

I have done this with DDR, DDR2 and DDR3, but it could also vary depending on Board manufacturer.