Does this PC3-8500 1066MHz DDR3 ECC DIMM work on the newest Mac Pro?

Go to Crucial or Macsales and find your model, or let their scanner check your RAM requirement.

I'm a little confused by the model no. you quote, but both sites would suggest that the PC3-8500 is correct.

the PC3-10600E is quoted for the 6-core and 12-core models, but may be compatible with the quad and 8-core also. However, if the original RAM is PC3-8500, you should match that (and the other way round of course).

8GB DIMMs don't work with others

2-3 x 8GB IS IDEAL

SDD 120GB boot drive

W3680 6 core 3.33GHz $620

(sell yours)

netkas.org tips on using PC GPUs

Another questions: The computer comes with 3 x 1GB. Can I take one chip out, then put 2 x 4GB in slot 1 and 2, and leave the 2 x 1GB in slot 3 and 4 to make it a total of 10GB?

I'm having difficulty finding a definitive answer to that one.

As far as I can judge, you can use 2x 4, 3x 4 or 4x 4GB.

ECC should be in matched sets, so 2x 4 and 2x 1GB may be ok, but as I said I can't find a definitive answer to that at the moment.

Until someone can give a more positive answer, I'd suggest removing all three 1GB and just using the 2x 4 for now. It's easy enough to put some back in if it transpires that it's viable.

Update;

It appears that matched pairs are ok, so you can put 2x 4GB in slots 1 & 2, and 2x 1GB in slots 3 & 4.

The pairs must be the same spec and manufacture.

Also, Lion appears to have a utility to check memory, so you should be able to see what combinations are possible.

2009 and later Nehalem and Westmere Mac Pros do not need matched pairs. They work well with 2, 3, or 4 DIMMs.

Optimum performance is with three of the same size, but the real-world penalty for using only two is under five percent, and the real-world penalty for using four is about five percent. Memory tests that unrealistically hammer on the memory (and do nothing else) will report slightly poorer performance with two or four.

8GB and larger DIMMs may not play nice with smaller sizes. So if you can see yourself going to really large sizes, buy fewer of the larger sized DIMMs now to avoid having to throw away the smaller ones, e.g., I expect to need 24GB eventually, so I should go with two*8GB today, and add the third 8GB (and possibly the fourth) later.

It is extremely complex to select the correct memories for these machines. Ask the Vendor to help you. Their "money back if it does not work for you" warranty provides the safety net you need. If the Vendor uses the "you buy it, you own it" method, shop elsewhere.

this vendor is also knowledgeable and helpful:

http://www.datamemorysystems.com/Mac_Pro_Memory.asp

Don't. Use one or the other, but don't combine them.