cMP 4,1 memory upgrade (1 stick only OK?)

[adam9c1]

cMP 4,1 Dual CPU unit

Currently I have four 8GB sticks in the machine. All sticks are 1.5v I belive
Can I add a single 16GB stick?
Am I "locked down" to 1.5v or can I install 1.3v?

Thank you.

 

[666sheep]

If these 8GB sticks are registered and if you must add this 16GB one – you can, but be aware that's non-optimal memory config. 1.35V will work fine together with 1.5V ones.

 

[adam9c1]

I had 4 sticks of 4GB registered and when I added 4 sticks of 8GB machine would not boot.
I had to take the original memory out.

So now I have 4 sticks of 8GB and would like to install a single 16GB stick.
I saw one for sale for $130 and of course can't find the link now...

 

[DougTheImpaler]

The memory will run at the slowest stick's timings/speed with the highest voltage (so the 1.35v memory will be run at 1.5v if you have some mixed in). This is OK as long as your lower-power stuff also supports 1.5v. Personally I have 2x8GB DDR3-1600 @1.35v and a 1x8GB DDR3-1600 @1.5v by mistake (thought I was buying another stick of the same RAM and I was wrong). All of that memory runs at 1.5v DDR3-1333, because that's what my CPU supports.

Try to balance the 3 channels to have as similar a capacity as possible. If you wind up with 2 bigger DIMMs and 2 smaller DIMMs, but the big ones in slots 1 and 2, and the smaller ones in 3 and 4. Slots 3 and 4 share the same channel on the memory controller, so that's what works best.

Worst case scenario, assuming the memory is good, is that on boot the memory configuration app will tell you to swap some sticks around.

 

[666sheep]

I had 4 sticks of 4GB registered and when I added 4 sticks of 8GB machine would not boot.
I had to take the original memory out.

So now I have 4 sticks of 8GB and would like to install a single 16GB stick.
I saw one for sale for $130 and of course can't find the link now...

Original (Apple factory installed) RAM is always unbuffered. This would mean that your 8GB sticks are registered. Check specs of your presently installed sticks before buying additional RAM. Just throw what you see on stickers in google.

 

[adam9c1]

Current ram is regular desktop ram from Frys.

 

[666sheep]

So, it's non-ECC, right? If so, you can't add single 16GB one. These are always ECC. All you can do is adding another couple of 8GB stick of non-ECC memory, unless you'd want to replace all of your RAM with ECC.

General rule: you can't mix ECC with non-ECC and registered with unbuffered.

 

[adam9c1]

Aha. Did not know that. Thank you.
So in theory I can max out at 64GB, or scratch the 32 I have and "start fresh".

 

[666sheep]

Best way to add another 16GB to your machine is 2x 8GB of memory matching specs with currently used one.