Just added more RAM... DIMM 2 on both risers shows empty?!

[Kingsly]

So I just got an extra 4GB of RAM in two 2GB matched pairs. I intend to get another 4gb for an even 8, but in the meantime 6 gb works.

The problem is that DIMM 2 on both risers appears to be faulty (haven't bothered to try 3 and 4). The new RAM only shows up if installed in DIMM 1 on each riser, in place of the factory RAM. Additionally, factory RAM does nothing in DIMM 2.

Are my riser boards faulty? MLB (I sure hope not)?

 

[chromatronic]

Non, its because mac pro dont take DIMM but FB-DIMM...
i asked yesterday about that before ordering....
so your ram will never work in the mac pro...
you need FB-DIMM

 

[Kingsly]

I have FB-DIMM. 800mhz, matched pair, Apple spec.
Something is up with the riser cards, since my new RAM works in slots 1. See the pic, DIMMs 2 on both risers A and B should show 1gb each of factory RAM.


FWIW, System Profiler still refers to RAM slots as being DIMMs. It doesn't make the distinction between fully buffered RAM or not.

 

[Umbongo]

You have it installed incorrectly. This how it should be:

Riser A slot 1: 2GB
Riser A slot 2: 2GB

Riser B slot 1: 1GB
Riser B slot 2: 1GB


Basically you fill A:1&2, B:1&2, A:3&4, B:3&4 starting with the largest DIMMS. The exception is if you only have 2 DIMMS they can go in slots 1 on each riser for improved performance and that is why Apple ship them that way. It's all in the manual if you need any more information.

 

[UltraNEO*]

You have it installed incorrectly. This how it should be:

Riser A slot 1: 2GB
Riser A slot 2: 2GB

Riser B slot 1: 1GB
Riser B slot 2: 1GB


Basically you fill A:1&2, B:1&2, A:3&4, B:3&4 starting with the largest DIMMS. The exception is if you only have 2 DIMMS they can go in slots 1 on each riser for improved performance and that is why Apple ship them that way. It's all in the manual if you need any more information.

Hence...

Page 46 of your MANUAL..

 

[Kingsly]

Aha. If someone would please fill out and mail the correct paperwork to have my intelligence license suspended, that would be greatly appreciated.

I've done Mac Pro RAM installs (correctly) literally hundreds of times while working both for Apple and for third party repair centres.
I have officially become an idiot.