Δαφνη Ευτυχια Αρθουρος

Once upon a time, I kept up on all the latest changes to the details of how computer components worked and related to one another -- all the different forms in which RAM was packaged (there were fewer then), the various disk interface standards, several common bus types, etc., and knew all the "that kind of machine takes this kind of memory and has that kind of floppy controller and has an address space of $foo, of which $bar is consumed by ROM..." for every machine I used or fantasized about. After many years of not keeping up with what the Hot New Machines were using because I couldn't afford 'em anyhow, and then getting old hand-me-down machines that had been Hot New Machines sometime after I stopped keeping up, and after a lot of new standards and variations being introduced, I'm waaaaay behind on my hardware knowledge.

Most of the time (*shrug*) I just fire up a new-to-me box, maybe swap the hard drive, make a note of what's in it, and install an OS, and don't get around to trying to upgrade. But once in a while I get an opportunity to upgrade (such as a friend dropping hand-me-down RAM in my lap), and being out of date bites me on the ass.

BoyGeorge, my Windows NT machine, has four SIMM slots and one DIMM slot. It used to have 32MB RAM in four 8MB SIMMs. At some point I was given a 64MB DIMM and put that in, but for some reason only got a total of 80MB. Now I've got a 256MB DIMM and a couple of 128MB DIMMs, and now that I finally cleared off enough tasks that I could power down the box, I was looking forward to making it swap a bit less often.

Okay, here's the confusion ... first, I think these DIMMs all came out of PCs (and my understanding is that even if they didn't, you can use Mac RAM in a PC but not vice-versa, right?). If I install the 256MB DIMM, POST reports a mere 7MB of RAM. If I install some of the 128MB DIMMs, POST reports 17MB RAM. If I install other 128MB DIMMs or any of the new-to-me 64MB DIMMs, the machine never gets past POST (in some cases it counts 32MB RAM and reports a memory error, and on other cases it never gets as far as putting any signal out through the video card). And, as noted previously, with the old 64MB DIMM it reports 80MB of RAM.

Where's my missing 48MB? And why is it so hard to match RAM to motherboard? (Okay, that last one's rhetorical -- what with different standards for error detection/correction, different voltages, different speeds, all using the same connector and usually without any useful information on a sticker or anything, there are too many standards ... But I still wanna know about the missing 48MB.) Can the address space of a motherboard be less than the address space of the CPU installed on it? Or is RAM slot wiring really bizarre?

(After I finish posting this, I'll shutdown and try the thing I forgot to try before: removing the SIMMs and just using the 256MB DIMM by itself. And then I'll try these DIMMs in various other boxes that have DIMM slots and need more RAM. Wish me luck.)