Anyone know why a Q840av has a RAM ceiling of only 128MiB?

#1 Tue, 8 Oct 2013 - 06:02

I ask purely out of academic curiosity, as my Quadra 840av has either 48 or 64 MiB in it now, don't recall which, which I am in no danger of getting close to the edges of either way. 128 megs is as big as a _single_ 72-pin SIMM can get, so why doesn't this machine support anything over 32MiB times 4? Is it just a ROM limitation, or is it like my Classic II in that the various motherboard components literally can't address anything past an arbitrary limit?

#2 Tue, 8 Oct 2013 - 09:40

Quadra 840AV with 512MB (128x4)

here is the link to that thread:

viewtopic.php?f=9&t=9282

the 128 meg simms that i bought worked fantastic in the LC475 / Q605 / PM6100

however i was not able to use these 128m simms in the LC3 or LC520 or LC550, i never tried them in the Q840av or LC575.

#3 Tue, 8 Oct 2013 - 22:11

Oho! Marvellous! Thanks for finding that. I now have Yet Another Project awaiting time and funding, and I love it!

#4 Fri, 18 Oct 2013 - 23:38

In my tests, 128MB SIMMs do not work in the Q840AV. However, search for bbraun's posts on the topic in the hacking forum. He's done some interesting RAM capacity increases with ROM modifications. I don't think he's done the 840AV, but my reading is out of date.