Installing MacPro5,1 Processor Tray into MacPro4,1

Epochmaker wrote:

I am tempted to find two 16Gb strips of 1333 ECC RAM and install them in slots 1 and 2, then move two of my 8Gb strips into slots 3 and 4.

According to reports you cannot mix 16GB memory with other sizes. Some reports simply flatly say it cannot be done but one particular issue is that 16GB memory is only available in 'Registered' form, whereas 4GB and 8GB can be either Registered or Unregistered and you cannot mix these types. I have not seen a means of determining what type existing 4GB or 8GB might be.

See http://blog.macsales.com/22745-mix-and-match-more-memory-faster-mac-pro-2

and https://www.macramdirect.com/macpro.html

The reason for going "registered" is that the raw chips available are not dense enough, so you need to have multiple chips with their outputs wired together on each output data bit. This produces too much Bus loading, and they will not work reliably that way. So you add the register.

When these were first introduced, there were some 8GB DIMMs that were Registered, but now only the 16GB DIMMs are that way.

I tried doing this the other day "for science".

I have a 2009 Mac Pro that has had it's firmware upgraded to 5,1 and I tried to put a 2010 CPU tray (both the 2009 and 2010 are dual CPU trays) into it. It will definitely boot up and run but the fans are run at full blast the entire time. This is likely a result of the two trays having slightly different temperature sensing units from their slightly different CPU/Heatsink setups. The 2010 tray is somehow confusing the 2009 and as a result runs that fans on full blast.

So in short, it is doable but the fans will blow loud and create a small wind tunnel in your home office. I wouldn't recommend it being a long term solution.

as something of an aside form what you were trying to do - I bet you could get someone with a 5.1 single processor to trade you for your 4.1 dual. A lot of people are looking for the 4.1 dual processor because they can swap the processors for xeon 6 core and end up with a 12 core system. That is what I am doing.

The answers will be in this thread:

http://forums.macrumors.com/showthread.php?t=1333421