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Sorry, I have heard that the procedure may has changed. I want to add 2x8GB RAM to the exisitng 2x4GB (Bank 0 and 1/DIMM O = slot 1 and 3 from the bottom). I may be wrong, but I was told to use the same amount of RAM/memory in each channel/bank, 12 in each, instead of same RAM. the pristine configuration (4GB Slot 1 and 4GB Slot 3 - iMac Late 2015) would validate this (regarding to dual channel). What is the correct configuration? Thanks a lot. BANK 0/DIMM0: Größe: 4 GB Typ: DDR3 Geschwindigkeit: 1867 MHz Status: OK BANK 0/DIMM1: Größe: 8 GB Typ: DDR3 Geschwindigkeit: 1867 MHz Status: OK BANK 1/DIMM0: Größe: 4 GB Typ: DDR3 Geschwindigkeit: 1867 MHz Status: OK BANK 1/DIMM1: Größe: 8 GB Typ: DDR3 Geschwindigkeit: 1867 MHz Status: OK
Usually you install in pairs to retain interleaving of the RAM. Apple does not mention your concern: https://support.apple.com/en-us/HT201191 Please give us a link to your concern. Standard RAM: 8 GB Maximum RAM: 64 GB* Details: By default, 8 GB is installed as two 4 GB memory modules (and two slots are unoccupied). *Officially, this model supports four 8 GB modules – one in each slot for a maximum of 32 GB of memory. However, as first discovered by OWC, it actually will support 64 GB of memory using four 16 GB modules. * RAM Type: PC3-14900 DDR3 Min. RAM Speed: 1867 MHz Details: Supports 1867 MHz PC3-14900 DDR3 SDRAM SO-DIMMs (204-pin).
From my experience - there isn’t much difference, as long as it works. The modules don’t even need to be in pairs. In my (rather sad) situation - I had to remove a perfectly functioning 8GB module from slot 2, because it causes lots of crashes. The slot itself is faulty - so now I run with 3 8GB modules. Less RAM, but no crashes. There is a good Memory-testing program called MemTest86 you can download for free, and use not only to validate your RAM modules, but also to benchmark your RAM performance, so you could re-order the modules to your liking and benchmark yourself.
