I recently bought a 2012 Apple Mac Pro tower and much of the information on customising out there wasn’t overly useful. With this in mind, I created a how-to video on how to install RAM into a Mac pro.
Just a note that Mac Pro’s require ECC (Error Checking) RAM.
The RAM installed was Kingston 1333MHz Ecc, 2x 8GB Sticks. (Part Number: KVR13R9D4/8I ).
Just something to mention, that the computer would not boot with both the stock Apple RAM and the Kingston RAM installed. The power light will flash indicating a memory issue. I have a feeling this is something to do with the stock RAM being unbuffered/unregistered and the new ram being buffered/registered.