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I've just upgraded my old mac pro 1.1 a1186 with 16gb of FB ram but only 8gb are recognized. I've tried different combinations in both risers but the result is always the same 8gb.
the ram is a Hynix 8gb (2x4gb) DDR2-667 PC2-5300F ECC Fully Buffered CL5 240-Pin
Mac Pro
you have a total of 8GB RAM in that image, possibly fully buffered RAM (5300F). Does it say ECC? If it's not ECC it may not be compatible, or the voltage may be different or the RAM is simply bad.
OWC is knowledgeable about Mac RAM
https://eshop.macsales.com/shop/memory/Mac-Pro-Memory#667-memory
the picture was related just to 2 of the four modules....i've checked every ram and seem to be fine. It's an ECC fully buffered.
The correct positioning is matched pairs in adjacent slots on the same riser-card.
That RAM appears to be hp Server RAM, which is intended for a computer whose fans are roaring away in a server room. If you do get it working, it is extremely likely to overheat and fail in your Mac, where the correct Heatsinks are HUGE multi-layered metal things so large that they barely allow space between them when installed. Your Mac pro is a Server-class computer, but is intended for an office environment where the fans are turned way down.
Your Mac Pro with Xeon processor uses its error-correction very aggressively at Startup. Any modules with any sort of errors during the power-On Self test will be listed as slots "empty" in this display:
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MacPro 1.1 a1186 Ram Issue
