PRAM and NVRAM differences and overlap with eachother and UEFI firmware chip

nvram

  1. Is PRAM stored on the same NVRAM chip that non-PRAM variables are stored. I always assumed that NVRAM was the UEFI firmware chip on the logic board. Are all of these one in the same (NVRAM – PRAM – UEFI firmware), basically are they all stored on the same chip?
  2. How do you set the PRAM variables like you set the NVRAM variables with the nvram command.

Thanks 🙂

Best Answer

Yes, PRAM is stored on the same NVRAM chip as the firmware variables, but it is managed separately. It actually shows up as a device in the firmware device tree.

HT1242: What's stored in PRAM

When you reset one, you reset the other.

HT1379: Resetting your Mac's PRAM and NVRAM

AFAIK, Apple has never supported direct developer access to PRAM, so it is not documented well (or at all). The functions readXPRAM and writeXPRAM can be used to access the raw bytes, although these days they are just wrappers around IOKIT functions which access the APL,MacOS75 partition in NVRAM.

The nvram command line program only manipulates the firmware variables stored in NVRAM, and so does not let you access the PRAM partition.

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