iMac memory issues
A while back I picked up an old iMac for next to nothing because it was broken, and I managed to fix it fairly easily. A friend on IRC sent me some “laptop RAM” that seemed like it’d probably fit it, and sure it does… 16GB! Unfortunately, Macs are famously picky and it does not seem to appreciate this RAM. Most of the time it works, but it might take one or two reboots to get it to actually function correctly.
Things like Finder, the System Settings, and so on will crash regularly when it’s unhappy. Sometimes, it won’t actually make it through the (agonizingly long at the best of times, due to a lack of SSD) boot process. Another friend on IRC mentioned they wanted it, so I figured I’d have a look at making it useful, after a Twitter thread about using improper memory modules in old Macs came up and I forgot about it until today. I spent the better part of a half an hour either side of dinner trying to find this old thread (which I thought was on Reddit, hence not finding it), but I managed to track it down eventually.
So after work, I pulled it out, plugged it in, and had a look at it. After some inspection, it seems that this technique will not help… it involves reading the SPD data, modifying it, regenerating the CRC, and writing it back to the chips to force newer DIMMs to be detected as older, slower ones. However that’s not the problem here: the iMac Mid-2011 supports RAM with a minimum speed of 1333MHz, and that’s exactly what this RAM detects as… so it’s likely related to timings, and I think it’s unlikely I’ll end up with a way to make it work satisfactorily.
While I was at it, had a look at patching the installer to drop Catalina on it. That’s a bust too! The GPU in this machine is much too weak to run Catalina acceptably, and it’d be borderline unusable. Apparently you can upgrade the GPU in these machines, but they use a special laptop GPU, and even something as weak as a GTX760M is over a hundred bucks on AliExpress! I don’t care about it that much.
So I figure if Greg still wants the machine, I’ll drop it off with him with the old RAM in place, and if he can stomach the reboots and stuff then he can use the newer RAM.