How to couple RAM Modules in iMac 27?

How to couple RAM Modules in iMac 27? Hi, I have just upgraded my iMac by adding 16GB (2x8GB) to the pristine 8GB (2x4GB). Since I know, but I may be wrong, that modules should be coupled, how do I have to do it?
Asked by: Guest \| Views: 314

Total answers/comments: 4

Comments display order:

bert [Entry]

Is possible that same RAM sizes should be in DIMMs and not in BANKs? Maybe apple just call them differently. Because here is screenshot how looks 12GB from factory in iMac.

bert [Entry]

"Sorry, I may be wrong, but I was told to use the same amount of RAM/memory in each channel/bank, 12 in each. the pristine configuration (4GB Slot 1 and 4GB Slot 3 - iMac Late 2015) would validate this (regarding to dual channel).

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"

bert [Entry]

"Correct! You want the SAME sized modules within the BANK.

Sadly, you have different sized modules within the BANK:

BANK0/DIMM0 has a 4GBBANK0/DIMM1 has a 8GB

Where you want:

BANK0/DIMM0 will have a 4GBBANK0/DIMM1 will have a 4GB

The other bank would be setup:

BANK1/DIMM0 will have a 8GBBANK1/DIMM1 will have a 8GB

Or you could go the other way were Bank 0 has the larger modules.

Note: The number after the word BANK thats the bank number NOT the DIMM number."

bert [Entry]

"I tried the same size = same DIMM configuration (as above comments suggested it would be quicker) and my machine wouldn’t boot. Turns on but screen stays blank. Had to revert to installing by BANK. Any suggestions as to why?

iMac 27’ retina late 2015

2x stock 4GB DDR3 1867Mhz

2x OWC 16GB DDR3 1867Mhz"