Mac Pro and ECC Ram, basic questions

If only a few errors then the user is not even notified.

However, if there are so many errors that they can't be correct that usually results in a kernel panic with many banks reporting errors.

Sometimes errors will be detected during the self test on startup and some times there will be a diagnostic led lit by the bad memory stick. Also if you open System Profiler/About this Mac and go to Memory part it will not say OK

Yes

Christian Stueben wrote:

Ok. So the sporadic "once-a-day" ram error that must be expected in a 128 gb machine will be corrected completely transparent. That is what i was hoping to read 🙂

Thank you!

greetings from germany

Chris

Single-bit errors in a word are detected by fast logic in the Xeon processor and are corrected, in Hardware, in one extended memory cycle. No software intervention is required, except that at low priority in the background, an error will usually be tabulated. No extra in-line software is executed and it does NOT generate an Interrupt (either of which would slow your computing).

One subtle twist is that the corrected data are NOT rewritten to RAM, so Reading that same location later will require a correction later (unless the corrected version is still in the processor cache).

Double-bit errors are detected, but most are not correctable. Uncorrectable errors will cause your Mac to HALT on a kernel panic, machine check, error overflow or uncorrected error, status 4 or 5, and almost always detected simultaneously by multiple processors. This is by design to keep such errors from poisoning your data.

The kernel panic reports are not identical, but are still fairly distinctive.

The error correction logic is used very aggressively at Startup. ANY errors that occur (correctable or not) during the very short time of the Power-ON Self Test will cause that module-slot to be declared "Empty" and it will not be used by Mac OS X.

if you see the some memory seem to be "missing" running

 menu > About this Mac > Report > Memory

(the same report lllaass posted above) ... may show those slots as "Empty".

The next time you start your Mac, the same test will be run again, without referencing any History, and the BAD modules may then test OK and be used. This does not mean they have healed! They should still be replaced.