Precision M6500: 11GB RAM possible?

Hello,

currently I have 12GB of RAM in my M6500, 2x4GB in slots A&B (underneath the keyboard) and 2x2GB in slots C&D (on the underside).
Recently I have bought a netbook with only 1GB of RAM and I'd like to upgrade it. Since I have no spare DDR3 modules and I don't actually need 12GB in my M6500 I thought about either swapping one of the M6500's 2GB-modules with the 1GB module in the netbook or leaving slot D in the M6500 empty.

Does anybody know if that would work? The Dell documentation is not absolutely clear about that. I have a table showing that 3GB is possible with 2+1GB in slots C&D but I don't know if that still applies if slots A&B are occupied too.

Of course I could remove both of the 2GB modules but sometimes I need a little more than 8GB of RAM so having at least 10GB would be nice. On the other hand I could just buy another 1 or 2GB module but I don't want to.

 

I mean as long as your machine POSTs and passes several rounds of memtest, I don't see the issue, though it is a funky amount of RAM.

 

Of course, if the laptop boots at all there shouldn't be any problem.
The thing is, I haven't tried yet and I'm pretty lazy. So it would have been nice if somebody could have told me for sure if it works or not.
If nobody can tell me I'll try it myself. But the M6500 is pretty choosy when it comes to RAM configurations.

 

Ok, I tried it and I'm officially confused.
First I swapped one of my 2GB modules with the 1GB module from the netbook. I would have expected to see 11GB (because every module is detected correctly), 8GB (because only the two 4GB modules underneath the keyboard are detected) or a non-working laptop (because the RAM isn't detected at all).
But what I see is 10GB, apparently because the BIOS maps 1GB for something I can't identify, which it didn't do before.

Then out of curiosity I completely removed this one module and saw 5GB. At least this seems somehow reasonable. One of the 4GB modules underneath the keyboard (e.g. in slot A) doesn't seem to be detected at all if the corresponding slot on the underside (e.g. C) is not occupied). This would match the statement of the Dell support that slots C&D have to be occupied to use slots A&B. The missing 6th GB is the BIOS-mapped one again.

 

Also don't forget that the speed of the RAM overall is the speed of the slowest stick of RAM.

Plus, you really want to try and match the RAM sizes so that you get the bump from interleaving.

 

I have 1066MHz modules installed while the 1GB module is 1333MHz so speed isn't an issue.
Also I don't care for dual channel since I've made the experience that it doesn't really improve my type of tasks. My bottleneck are the HDDs or the CPU.

Thanks anyway for the reminder!

 

If you have an even number of sticks, you're already running dual channel.

 

Even if they are not the same size? How can the portion of the bigger stick that has no counterpart on the other stick run in dual channel?