Installing MacPro5,1 Processor Tray into MacPro4,1

I am a little late to this party so please excuse me. I have just upgraded a Mac Pro 4.1 to 5.1 firmware and installed a single X5675 3.06 Ghz 6 core processor without a hitch. That took the Geekbench score from 7,100 to 14,900 with the help of 24Gb in 3 sticks, slots 1, 2 and 3. Used ECC 1333 RAM. The memory is running at 1066Mhz, I understand that a minimum X5680 processor is required to see the memory run at 1333Mhz.

I tried running 32Gb of memory but the Geekbench score was only 14,200, a loss of 700 points. I haven't tried x2 4Gb strips of RAM yet.

One other thing to note; in order to install the FW update you need to run a *pre* El Capitan OS. The SIP (System Integrity Protection) prevents alterations to the firmware except by meddling with terminal... Which I generally avoid if there is a viable alternative.

14,900 / 14,200 = 4.9 percent slowdown, which is right in line with the predicted penalty for running four DIMMs instead of the optimum 3 for these Macs.

But if you need a little more than 24GB, that extra RAM will be worth having (even at 5 percent slower) rather than paging to disk.

Thank you Grant, useful info. I somehow doubt I will notice a 5% hit on performance, I am expecting that 99% of the time the computer will be waiting for me! 😁

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.

I am assuming that will make little or no difference to my Geekbench score but may improve the real life performance under intensive use?

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.