Can you run a DP 4,1 with a single CPU?

[tpivette89]

As the title states, I have a dual processor 2009 Mac Pro (flashed to a 5,1). Currently running the stock E5520 CPUs (4-core 2.26ghz). I have a single X5677 that I have successfully de-lidded, and a second one on the way (maybe a week or 2 out). Can I run the dual CPU tray with just 1 CPU installed while I wait for the second one to arrive? If so, which socket do I have to place it in?

I have Macs Fan Control if some of the fans start acting crazy due to a CPU missing.

 

[flowrider]

Yes, but the fans will go crazy unless both sockets are filled. If you only run run, it needs to be run in socket "A". If installed in socket "B" it won't work at all. Assuming Macs Fan control will take care of the fan situation, but have never tried that.

Lou

 

[tpivette89]

Yes, but the fans will go crazy unless both sockets are filled. If you only run run, it needs to be run in socket "A". If installed in socket "B" it won't work at all. Assuming Macs Fan control will take care of the fan situation, but have never tried that.

Lou

Cool, thanks for the info. CPU socket A it is. Will give this a try later and see if Macs Fan Control handles it or not.

 

[MisterBiro]

Yes, but the fans will go crazy unless both sockets are filled. If you only run run, it needs to be run in socket "A". If installed in socket "B" it won't work at all. Assuming Macs Fan control will take care of the fan situation, but have never tried that.

Lou

In my experience that didn't quite happen.

I ran my dual 4,1->5,1 with a single CPU (I didn't install the HS on socket B), and didn't have any issues with the fans, they ran as normal.

 

[h9826790]

MacsFanConrol may work actually, worth to try.

My understanding is the lost of CPU B temperature makes the SMC command full fan speed just in case the CPU is actually hot but sensor not working properly.

Since MacsFanControl can override the target fan speed. It may able to make the fan behave “normally” (if you make all Intake / Exhaust / Booster fan speed base on CPU A diode temperature, e.g. min 70C, Max 90C etc.)

 

[tpivette89]

In my experience that didn't quite happen.

I ran my dual 4,1->5,1 with a single CPU (I didn't install the HS on socket B), and didn't have any issues with the fans, they ran as normal.

Awesome! By any chance, do you remember if you had the heatsink installed (plugged in) for socket B even though there was no processor there?

EDIT: just re-read your response and it seems as though you did NOT have the 2nd heatsink installed.

I have the machine torn apart as we speak getting ready to test everything out. Will update when things are back together.

 

[h9826790]

In my experience that didn't quite happen.

I ran my dual 4,1->5,1 with a single CPU (I didn't install the HS on socket B), and didn't have any issues with the fans, they ran as normal.

That doesn’t sounds normal. It’s a well known behaviour that the fan will run at full speed if CPU B is missing. This is actually a fail safe mechanism.

 

[tpivette89]

Finished up the install... removed the old E5520s and replaced them with a single X5677 in socket A. Fan speed went nuts, and using Macs Fan Control, I determined it to be because CPU B was not occupied. Made a couple tweaks to the fan speeds, and all was well.

One thing I noticed was the single CPU was running hotter than normal... with the E5520s installed in a pair, CPU A temps usually idled at 102*F. With the single X5677, idle temps were around 112*F. Even with the dual X5690s I had in there before, idle temps never rose above 105*F. Maybe this will adjust and go down when a 2nd CPU is installed.

Geekbench scores were fantastic (single core):

https://browser.geekbench.com/v4/cpu/10499150

I know this will drop (single core) when the 2nd CPU is added, but this reading (even at the higher temp) beat out my X5690 in a SP machine:

https://browser.geekbench.com/v4/cpu/8005381

Either way, it's safe to say you can run a single processor in a dual CPU machine effectively without major compromise. Can't wait for the 2nd CPU to arrive to see the results!

 

[MIKX]

Before I replaced my tray I too had just one CPU in A .. it ran with fans at normal speed.

 

[MisterBiro]

That doesn’t sounds normal. It’s a well known behaviour that the fan will run at full speed if CPU B is missing. This is actually a fail safe mechanism.

It definitely didn't do that for me, and as far as I can tell all the fans work as expected now it has both CPUs installed again.

 

[h9826790]

It definitely didn't do that for me, and as far as I can tell all the fans work as expected now it has both CPUs installed again.

Before I replaced my tray I too had just one CPU in A .. it ran with fans at normal speed.

No fan control software pre-installed?

 

[MisterBiro]

No fan control software pre-installed?

No, fresh, stock Mojave install.

Unfortunately I've upgraded the boot ROM since then, so I can't retest.

 

[fhturner]

One thing I noticed was the single CPU was running hotter than normal... with the E5520s installed in a pair, CPU A temps usually idled at 102*F. With the single X5677, idle temps were around 112*F. Even with the dual X5690s I had in there before, idle temps never rose above 105*F.

So, you started with E5520s, went to X5690s, then back to the E5520s, and now to X5677? Why not just stick with the X5690s? Did we talk about this in another thread, perhaps about selling for the cost differential? If so, seems like a whole lot of work for a fairly small savings...

 

[tpivette89]

So, you started with E5520s, went to X5690s, then back to the E5520s, and now to X5677? Why not just stick with the X5690s? Did we talk about this in another thread, perhaps about selling for the cost differential? If so, seems like a whole lot of work for a fairly small savings...

Because I LOVE to tinker and try different things with my computers. I don’t use my computer for work or any type of business, it’s purely a hobby.

Swapping CPUs in my dual processor machine takes less than 10 minutes... thats tray removal, heatsink removal, cleaning old thermal paste, and the reinstallation of everything. Not much time or effort for me at all and I enjoy doing it.

I already sold the X5690s... bought the pair about 6 months ago, delidded them, and ran them for a little while. I sold them for a profit, so I won’t miss them. Hell, in a year if I decide the X5677s aren’t enough for what I may be doing with the machine at that time, I may go back to the X5690s. They may even be cheaper then! Or I’ll try something different, who knows. That’s half the fun for me.