Triple channel memory setup

I currently have a server with 18 memory slots

 DIMM_A1  DDR3-Registered 4096 MB
 DIMM_A2  DDR3-Registered 4096 MB
 DIMM_A3  DDR3-Registered 4096 MB
 DIMM_A4  [Not Occupied]  
 DIMM_A5  [Not Occupied]  
 DIMM_A6  [Not Occupied]  
 DIMM_A7  [Not Occupied]  
 DIMM_A8  [Not Occupied]  
 DIMM_A9  [Not Occupied]  
 DIMM_B1  DDR3-Registered 4096 MB
 DIMM_B2  DDR3-Registered 4096 MB
 DIMM_B3  DDR3-Registered 4096 MB
 DIMM_B4  [Not Occupied]  
 DIMM_B5  [Not Occupied]  
 DIMM_B6  [Not Occupied]  
 DIMM_B7  [Not Occupied]  
 DIMM_B8  [Not Occupied]  
 DIMM_B9  [Not Occupied]  

I want to add an additional 12GB of ram to the server, can i just put 3 more sticks in either A4-6 or B4-6 or would i need 6 sticks.
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That depends  a lot on the server.

Some servers require the larger sticks to be in the first slots, others in the last.

Your vendor should have detailed information on the correct way to populate the slots
CaptainGibletsAuthor Commented:
it is a dell poweredge T710 server.

Can't find much info on their site and need order it asap.
CaptainGibletsAuthor Commented:
Also, for some unknown reason the 8gb chips are cheaper than the 4gb chips

However i can't use the 8gb chips unless i replace all the 4gb chips can i? Or can i use 6x 4gb on B1-6 and the 3x 8gb on A1-3
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Check page 98 at

all populated memory channels must have identical configurations.
In a dual-processor configuration, the memory configuration for each processor must be identical.

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Gary CaseRetiredCommented:
The key point is what's quoted above:  " ... In a dual-processor configuration, the memory configuration for each processor must be identical ..."

So, assuming this is a dual processor server,  you'll need to add 6 modules.

As for mixing size -- you can do that, but you'll have to buy two more 4GB modules, and 4 of the new size.    Then you can realign the modules so you meet the requirements noted in the manual (as noted above, these are shown starting on page 98).
CaptainGibletsAuthor Commented:
Well, i purchased 4x 4gb memory sticks, and installed them into bays A4/5 and B4/5

Server boots fine, but i get 40gb installed but only 32gb usable.
CaptainGibletsAuthor Commented:
Obviously forgot about 32gb limit on standard server, luckily my other server needs a memory upgrade as well haha!
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