in Mac Pro Server dual-Processors, if one processor go down another one works fine ?

I think you'll have a kernel panic at the point of a CPU failure even if you do have a second processor. Dual CPU's in Mac Pro's are for intense workloads not redundancy.

To be honest I've never had a CPU fail in any of the multi-processor Mac Pro's and PowerMacs I've work on over the years so I can't say for sure. Maybe someone else has experience of this.

Hope this is of some help.

Rich.

Rich is correct. I have an old MacPro with one bad (flakey) processor. The system will generally run pretty well, but occasionally the bad processor will cause the system to panic.

It means the system is usable, but you can't really trust it because it can panic at any moment.

Some high end servers do have the ability to disable a single faulty CPU but none of Apple's computers (or servers) has ever had this ability. In otherwords if a single CPU fails the entire system is going to crash.

I once bought a used PowerMac G4 MDD Dual-processor, bootability "unknown", for a song. I saw kernel panics on boot; booting in verbose mode, I could see an entry with "CPU" so I figured at least one CPU was toast. I could a System 9 CD though. 😀

Those were open firmware Macs, and there was a way to shutdown the second CPU in open firmware, which I did. After that, it started up and worked fine -- I eventually bought a replacement board cheap. Back in then around 10.4-10.5, the Developer tools also included a CPU System Preference which let you turn off a CPU on a dual-CPU system; but the trick to getting there was whether you could actually boot to get to the desktop.

So getting back to today. I don't know whether the current Developer Tools still include that CPU System Preference for shutting manually a CPU on a dual CPU Mac. And with the shift to EFI, I don't know whehter there's someway to drop down into it to shutdown a CPU, like you could in open firmware.