Firmware Update: Firmware Updates 4.1.7 and Later May Disable Out-of-Spec Third-Party RAM

This article describes why some third-party RAM (memory) may no longer be recognized by the computer after installing the 4.1.7, 4.1.8, or 4.1.9 firmware updates for iBook, PowerBook G3 and G4, Power Mac G4, Power Mac G4 Cube, and iMac.
This article has been archived and is no longer updated by Apple.
The Apple 4.1.7, 4.1.8, and 4.1.9 firmware updates incorporate a number of fixes that dramatically improve system stability and performance. The update also includes a check that validates whether the memory installed in the computer is compatible. This check was added to help alleviate random crashes and stability issues. This memory test disables memory DIMMs that are found to be out of specification, and DIMMs that cannot be determined to be compatible. As a result, some third-party memory that was recognized by previous versions of firmware may no longer be recognized after the updates.

With this set of firmware updates, Apple is strictly enforcing adherence to published RAM specifications. RAM that falls outside of specification can cause stability issues with Apple hardware and software, including Mac OS X. If out-of-spec RAM is installed in a Macintosh computer, the system cannot be expected to perform reliably. Apple has provided RAM specifications to memory developers for some time.

When purchasing RAM modules for use in Macintosh computers, make sure that they conform to the JEDEC specification. Check with your memory vendor to ensure that the RAM module supports the correct timing modes and that their Serial Presence Detect (SPD) feature has been programmed properly, as called out in the JEDEC specification.

If you have installed the 4.1.7, 4.1.8, or 4.1.9 firmware update on your computer and some of your third-party RAM is not recognized, contact the vendor of that RAM.
Published Date: Oct 7, 2016