MP 1,1-5,1 Ram not working together?

[tampano]

Hi everyone,
just a confirmation of something i didn't check before buying. These two types of RAM won't work together because of the speed, right? If I put two pairs of each in a Mac Pro 5.1 all I get is a flashing LED. Single pairs work perfectly, tried also in different positions.

 

[TheIguana]

The bottom one is Registered RAM the top one is unregistered, that’s why they won’t work together.

 

[Snow Tiger]

speed isn't the issue , as the System will reduce memory speed to the lowest common denominator of the installed modules . Everything else being compatible .

But you cannot mix registered ( buffered ) and unregistered memory modules in the same System , even if they are compatible separately in a System .

It is a good rule of thumb to install only matching memory modules .

Also , avoid the use of Quad rank and 32GB modules in a Nehalem cMP .

For high performance , install only three matching memory modules ( in the four slotted ) CPU bank , per CPU .

Here is a list of known good 1333 MHz modules for your Mac :

16GB = Samsung M393B2G70AH0-YH9 .

16GB = Samsung M393B2G70BH0-YH9 (low voltage) .

16GB = Micron MT36KSF2G72PZ-1G4 ( low voltage ) .

16GB = Samsung M393B2G70BH0-YK0 (1600 MHz) . Downscales to 1333 MHz .

16GB = Nanya NT16GC72C4NB0NL-CG ( low voltage ) .