Mac pro RAM

RAM must be installed in matched pairs. One on Riser A and the other on Riser B in the same slots. Sounds like that isn't what you did.

Must be the preferred arrangement for your model.

Only if there is ONE set, and you have a 3,1 does RAM go "one on Riser A, one on B" otherwise all FBDIMMs have to go in pairs on same Riser (there are weird off the book, not by the book) where it doesn't work and where slot 2 seems to be an issue, in which case one set in slots one and another set in slot three, splitting the set across Risers. Not standard.

How To Install and Remove Memory Mac Pro

https://support.apple.com/kb/HT4433

Mixing brands can be an issue. 667MHz 2 x 2GB sets go for $30 on Amazon.com and I have now got 4 x 2GB in mine and they run colder and seem to be better quality than any I had previously.

2x2GB FBDIMM DDR2 667MHz @ $30

http://www.amazon.com/BUFFERED-PC2-5300-FB-DIMM-APPLE-Memory/dp/B002ORUUAC/

Apple link does that. OWC MacSales has one but that is aimed at 2008 which is different (slightly).

Note: DIMMs must be installed in pairs of equal size from the same vendor. For instance, you must not have one or three DIMMs on either riser at any time. Additionally, two DIMMs from different vendors should not be combined and used as a pair.

Mac Pro 2006-2008

2008 Mac Pro Memory Arrangement

http://eshop.macsales.com/Customized_Pages/Framework.cfm?page=install_videos/mac pro/macpro_quicksheet.html

Maybe you have a defective Riser. Rare but happens.

Risers

http://www.dvwarehouse.com/Apple-Memory-Riser-card-for-Mac-Pro-First-Generation- 922-7695-----NEW-p-37247.html

http://www.powerbookmedic.com/Mac-Pro-Memory-Riser-p-17711.html

I didn't say anything Apple doesn't and from 7 yrs using and owning a 1,1.

There needs to be RAM in top Riser "A" even if it means swapping Risers.

Yours may work fine with brand A only, or brand B only, but not when A and B are both present.

Find which sets are defective and/or incompatible - it happens. Kcomputerbay is fine but sometimes people have gotten a set that did not work with other brands or got a bad set.

http://www.amazon.com/Komputerbay-PC2-5300F-Buffered-FB-DIMM-Heatspreaders/dp/B0 05HIWD5U/

Hey I'm having a similar issue with my mac pro 1.1 . I have 2 pairs of 2GB and two pairs of origional 512mb for a hypothetical total of 10GB. I have tried every possible configuration in attempt to get all the ram working but it just won't happen. Here are some examples of my results:

Top Tray, riser A:

DIMM1: kingston 2GB ddr2 667Mhz FB

DIMM2: Empty

DIMM3: kingston 2GB ddr2 667Mhz FB

DIMM4: Empty

BOTTOM TRAY, Riser B:

DIMM1: kingston 2GB ddr2 667Mhz FB

DIMM2: Empty

DIMM3: kingston 2GB ddr2 667Mhz FB

DIMM4: Empty

=8GB fully functional. This is the configuration I have setteled on for now.

Top Tray, riser A:

DIMM1: kingston 2GB ddr2 667Mhz FB

DIMM2: kingston 2GB ddr2 667Mhz FB

DIMM3: apple 512mb ddr2 667Mhz FB

DIMM4: apple 512mb ddr2 667Mhz FB

BOTTOM TRAY, Riser B:

DIMM1: kingston 2GB ddr2 667Mhz FB

DIMM2: kingston 2GB ddr2 667Mhz FB

DIMM3: apple 512mb ddr2 667Mhz FB

DIMM4: apple 512mb ddr2 667Mhz FB

=5GB functioning, only from riser A

I'm going to go through the different configs again and grab some screen shots to share but if anybody has any ideas in the meantime, I'd love to hear them.

BTW, yes, all ram tests as good, as do the risers.

Thanks!

When the memory is on the bottom tray it won't boot

It must have SOME memory on the top tray, or it can't boot.

I would say, don't even bother trying to use 512MB DIMMs they just take up a DIMM slot and add heat and should be replaced with 2 x 2GB kit for $30.

Interestingly enough, I have gotten mine to boot and run with just the bottom riser in. However, only slots 1 and 3 are recognized. Weird stuff.

That makes sense. Ultimately, I would like to get the 8x4GB of Kingston ram that I got fully functioning. But that's a whole other mess where the ram is only recognized as 2GB sticks instead of 4. I'm pretty new to Macs but have successfully upgraded my newly acquired Mac Pro 1.1 to an 8 core machine running mountain lion. More updates soon!