MP 1,1-5,1 Mac Pro 3,1 56GB RAM installed, only 52GB seen?

[r6mile]

Hi,

So in order to avoid the known slowdown of SSD speeds in a 3,1 Mac Pro, I decided to install 56GB of DDR2-667 RAM, which I understood would be the maximum without any modifications. This is installed as 6x8GB and 2x4GB RAM. However, for some reason only 52GB are seen - basically the 4GB sticks are only seen as 2GB sticks. If I take out a pair of the 8GB sticks, the 4GB sticks are seen properly. Is there something I haven't understood?

 

[joevt]

If you install 64 GB, then you can use the maxmem=63488 boot arg to avoid the slow down problem. Windows has a setting in the BCD to do the same. Linux does this automatically.

There is an issue with the dosdude1 patchers for installing unsupported versions of macOS which erases the boot-args. A modification can be made to avoid that.

 

[Ludacrisvp]

Are any of the DIMMs quad ranked?

 

[r6mile]

If you install 64 GB, then you can use the maxmem=63488 boot arg to avoid the slow down problem. Windows has a setting in the BCD to do the same. Linux does this automatically.

There is an issue with the dosdude1 patchers for installing unsupported versions of macOS which erases the boot-args. A modification can be made to avoid that.

Thank you, yes I knew about that fix but I was trying to avoid messing with that.

Are any of the DIMMs quad ranked?

No, all of the RAM is Kingston 2Rx4 PC2-5300F. This issue has me stumped! I've tried PRAM reset but no luck.

 

[doobydoooby]

Have you changed the siting of each stick? I remember a couple of occasions where my 3,1 wasnt seeing a stick because of its location even though it followed the rules and the whole thing was fixed just by shuffling them around.