According to memtest86, there is a persistent single bit error in my MacBook Pro's 16GB of DDR RAM.

Since the error is in the second half of the physical address space, I can work around the problem by running sudo nvram boot-args="maxmem=8192". However, this is a bit of a waste of the other half - a working 8GB minus one bit.

Is there a way, perhaps with an Open Firmware command or configuration, or a special boot-args option (e.g. nvphash?), that will allow me to mark as unusable just the small section that contains the bit error?


1 Answer 1


You can achieve what you want with the system call mmap(2) passing as argument for the protection value PROT_NONE which means pages can't be accessed.

But I would suggest to buy a new memory chip, because the error you detected is the signature of bad quality and your erroneous bit won't stay alone for too long (within the same chip).

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