I've had 128 GB (4x32 GB) installed on my Mac Pro 6,1 for years, and suddenly the computer doesn't recognize all 128, it only recognizes 96. It is Mushkin iRAM and haven't had any problems with it before.
If I re-seat the RAM, it will alternate between DIM 2 and DIM 4 not recognizing (I did 2x full reseats). Point being, the RAM itself appears to be OK.
Resetting the PRAM didn't work either.
Any ideas?
Mac Pro
Totally. When I got the RAM to recognize it wasn't showing any errors. It was just alternating which slots were reading and which weren't. Some weird bug with DIM 02 and DIM 04.
In the end, an OS update got them recognizing (again). I was running some old Mojave Beta and forgot about it. All good now.
I will update here if the bug pops up again.
Unless your Mac was unrealistically HOT, those DIMMs are Bad, and their problems will be back.
Because of the way they are tested again at each startup, they may pass this time, and fail the next time (or similar).
But problems do not fester. When present it is either good, having simple error corrected, or the computer halts on a distinctive kernel panic, machine check.
User Tip: Mac Pro and Error Correcting Co… - Apple Community
Especially the last paragraph, which explains why some of your RAM disappears.
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Mac Pro RAM Not Recognizing?
