Adding new memory to stock iMac

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When adding more memory to stock iMac, do I keep the stock memory too? Is the system slot sensitive. e.g. mix 8 gb dims and 16 gb dims. Any particular order?
 

Cory Cooper

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Hello and welcome.

-Which exact model iMac?
-How many slots does it have?
-How many and what sizes are already installed?

You can mix sizes, but most iMac models use memory interleaving, so you want to add RAM sticks in pairs. For example, if your iMac has four slots, and the original Apple RAM occupies two slots - i.e. two 2 GB sticks, you can add a pair of 4 GB in the remaining two slots, and it will work fine. It depends on the model, number of slots, type and size of RAM sticks, etc.

C
 
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I have ordered a new IMAC 27" it comes with 8 GB. I have also ordered 2 X 16 GB Dims. All to be delivered soon. Someone said to stagger the new and existing memory. Is this correct?
 
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I have ordered a new IMAC 27" it comes with 8 GB. I have also ordered 2 X 16 GB Dims. All to be delivered soon. Someone said to stagger the new and existing memory. Is this correct?
Leave the fitted memory where it is and use the 2 empty slots for the 16gb sticks.

my imac came with 8gb fitted (2 x 4gb) 4gb in Bank0/Dimm0 and Bank1/Dimm0, I fiited another16gb (2 X 8gb) 8gb in Bank0/Dimm1
and 8gb in Ban1/Dimm1.

Bank0/Dimm0 = 4gb
Bank0/Dimm1 = 8gb

Bank1/Dimm0 = 4gb
Bank1/Dimm1 = 8gb
 
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