Table of Contents for this issue:
Re: Performa 405
Re: 32-Bit Clean and MODE32

The Performa has 6 MGs of RAM (expandable by Ram Doubler) and now plenty of hard drive space. I plan to run a 7.5 system on the Performa, but am capable of running up to a 7.5.5 if necessary.

I would never run anything beyond 7.1 with that small amount of memory. Per GURU you can upgrade with 12meg of memory but only a maximum of 10meg can be addressed by that machine. The cheapest upgrade that you could do to get more use out of that machine would be to add memory. At 10meg a stripped down version of 7.5 would be workable. The real trick to getting full use out of an old Mac is to not ask it to do more than it was really intended to do. Good Luck....

Always Apple!, Michael

So although I've come across references to "Mode 32" in some threads from various items (other newsgroups, and occasionally in a description on shareware), I'm not too sure what it really means. I've also come across the phrase "32 bit clean" and I'm not exactly sure what that was referring to either.

It's easy to get the 24/32-bit issue confused with graphics (the number of colors on the screen).

32-bit addressing is really referring to how much memory the computer can access. Since each bit of memory needs a _unique_ address, Apple gives each a number. The problem is that in Apple's original Macintosh design they used a 24-bit number (a binary number 24 digits long) for memory addressing. Since the largest number capable of being represented by a 24-bit number is 16.7 million, this meant that memory could range from address 1 to 16 million, meaning that 16 megabytes was the _maximum_ the operating system could access. Keep in mind this was back when the 128K used in the first Macintosh was considered a monstrous amount of memory, so it didn't seem like such a limitation. In fact, Apple limited it even more, by assigning some of the "excess" memory addresses to the ROM of the computer, some for each of the expansion cards in the computer. So in reality the maximum memory a System 6 Mac could access was 8 megabytes.

With System 7, Apple began using a 32-bit number for memory addressing. A 32-bit number can represent over 2 billion... meaning today's Macs could theoretically (if you could get it in there) access 2 gigabytes of RAM!

Unfortunately, not all software is compatible with 32-bit addressing. Using incompatible software causes disasterous crashing. (Compatible programs were called "32-bit clean".) Even more unfortunately, Apple discovered some of its _own_ software was incompatible--namely the ROMs of early computers like the Mac II and SE/30. Without a ROM upgrade these computers wouldn't run 32-bit addressing. In fact, Apple was looking at major lawsuits because of these "dirty" ROMs.

Then along came Connectix. They had a great deal of experience with memory issues based upon their writing of programs like Virtual (a virtual memory program) and Maxima (RAM disk software). In fact, they'd already figured out a way past the 8MB limit--they would "steal" the unused addresses by empty slots in your machine (remember Apple reserved 1 MB for each slot) and let your real or virtual memory use them. (For example, if you only had 256K ROMs in your machine, the OS still reserved a full megabyte of addresses for the ROM. Connectix's Virtual could steal these extra addresses and map them to real or virtual RAM. Very clever.)

Anyway, Connectix created a little program called Mode32 that fixed the dirty ROMs on older Macs, letting them run in 32-bit mode. Without Mode32 an older Mac cannot access more than 8 MBs of RAM (unless you use Connectix's stealing method, and that's limited to 14 megs). Mode32 was such a terrific little program--a simple control panel with an on/off switch--that Apple bought the rights to it and gave it away free (and avoided costly lawsuits and/or millions of ROM upgrades).

To show you how the program works, here's an example: Just yesterday I installed 16 megs of RAM in an SE/30. It reported 17 megs installed when booted up (there was already a meg on board) but the System Software bar reported 10 megs in use leaving only 6 or so free. I installed and turned Mode32 and switched on 32-bit addressing and rebooted. Bingo, 15 megs free (2 used by the system).

I personally have run Mode32 on my Mac II for 5 years or so without any real problems. I have 20 megs in my machine. The only incompatibility I've found is my Mediavision nubus 16-bit sound card... the card works fine in 24-bit mode, but when I boot with Mode32 installed the Mediavision software tries to tell the card to work in true 32-bit mode (hardware) and crashes. Mediavision blames Connectix's Mode-32. Connectix tells me they had a simple patch to Mediavision's software that fixes the problem, but they can't give me the fix because they gave it to Mediavision. Mediavision denys having this patch. Each company points at the other one and neither will solve my problem. Very annoying.

The upshot is that I can use my sound board but only have 8megs of RAM available, or I can have 20 available but not use the sound board. Stupid, eh? (Especially since my main interest in the sound board is to record movies with sound, and recording movies requires _lots_ of RAM to get a decent frame rate.)

Anybody out there have any ideas how to solve this problem? :-)

--Marc