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Mac OS 9.2.2 Memory Limit of 1.5 GB... Some Answers

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nightstalkerpoet:
Thanks, I'll take a look at those!

From reading this page, it appears that the potential conflict could be in a REALLY stupid place - fonts.
https://68kmla.org/forums/index.php?/topic/38338-crazy-ram-in-9600/

I got there simply due to a curiosity of the PowerMac 9600 and Ram.

If 256mb EDO Ram was installed (https://harddiskdirect.com/228471-001-compaq-256mb-edo-ecc-60ns-168-pin-dimm-memory-module.html) in that system, you'd have access to 3gb of ram. I've read MDDs don't like any more than 2gb (though there's potential there for up to 4gb), but maybe the 3gb limit could be pushed in these models for RAM intensive operations that don't require as much speed.

nanopico:

--- Quote from: nightstalkerpoet on January 05, 2018, 10:57:25 AM ---Thanks, I'll take a look at those!

From reading this page, it appears that the potential conflict could be in a REALLY stupid place - fonts.
https://68kmla.org/forums/index.php?/topic/38338-crazy-ram-in-9600/

I got there simply due to a curiosity of the PowerMac 9600 and Ram.

If 256mb EDO Ram was installed (https://harddiskdirect.com/228471-001-compaq-256mb-edo-ecc-60ns-168-pin-dimm-memory-module.html) in that system, you'd have access to 3gb of ram. I've read MDDs don't like any more than 2gb (though there's potential there for up to 4gb), but maybe the 3gb limit could be pushed in these models for RAM intensive operations that don't require as much speed.

--- End quote ---

Well the OS knows about all 2 GB, but it is only assigning 1.5 to the process manager and the rest is assumed to be system memory by the OS, mapped or unmapped.  Part of the view right now is that the process manager may not be able to handle two seqments of RAM. One option is to somehow give the process manager all the RAM, but mark the 68k emulator as not usable and leave it alone.   

256 EDO in the 9600 wouldn't work afaik.  It limits each dimm to 128.  Limit of the hardware memory controller (not the MMU in the CPU).
Same goes for the MDD.  The memory controller can only handle 2GB.  It's a hardware limitation on those machines.

ELN:
The NK knows about all 2 GB but is instructed by the Trampoline via the ConfigInfo structure to allocate a maximum of Ox5FFFE000 to the primary address range (PAR). The upper layers are informed about the leftover physical memory via the SystemInfo structure, but can only access it indirectly by asking the kernel to map it into the logical address space.

The PAR is limited to that size because of some fixed-address data structures that the upper layers expect to find in the 5 and 6 segments. The kernel gets instructed to create these, too. The infoRecord page at 5FFFE000 can be moved with a few patches to the system, but the structures and code a bit higher up are too deeply rooted to move.

darthnVader:
You know, many years ago I remember reading and article that technically the G4 could address 4 GB of Ram, but there was some catch to it, and I forget the exact terminology used, so bear with me.

It had something to do with using 4 GB only 2 GB could be made available due to some flaw in how the G4 was made, or how it worked. Something like the other 2 GB could only be addressed as "Shadow" memory, or "Backside" memory?

I don't think latter chips like the 7447/4478 were even made at the time the article was published.

So, maybe, hope beyond hope, later G4's could address unto 4 GB of Ram?

Something similar to PAE?

I mean, with OS 9, virtual memory is disabled with over 1 GB of ram, but OS X can use VM with over that. If we could get it to work, at least partition it as a RAM disk, and run our VM on that RAM disk?

adespoton:

--- Quote from: DieHard on August 25, 2016, 08:32:56 AM ---Like I mentioned, running a studio under OS9 in the box will definitely run out of RAM at one time or another. 

Yes, G4s are cheap, but having multiple noisy G4s with extra cables and monitors are NOT the answer for many users; it may look cool, but many musicians have very little space due to nagging wives and other family obligations and most of the time are crammed in a small corner of the den as the "DAW cave".

So, I really believe, any efforts of maximizing OS 9 to "squeeze" more out of it, are not in vain.

Besides, it's fun to do what the Pros would not do... you act like that had a choice, they were hired employees that signed non-disclosures and were specifically told what to code, and what not to code.  Even if it was changing only a relative small amount of code to raise the RAM ceiling, I doubt any programmer that was making good money would make that argument with management.  They did as they were told, not as they wanted to... so to imply that "the pros couldn't do it, so how can we", may not be an accurate assessment of the facts.

--- End quote ---
Indeed.  Many of the fixes for OS 9 are actually fairly well understood in certain circles.  The issue here was that Jobs was burying OS 9 to drive sales of OS X and simplify the engineering chain.  So most of the people with the access and expertise to fix the problems... were moved elsewhere.  Must be frustrating for some of them, to know what the bugs were, what the proposed fixes were in the pipeline, and not only not be able to fix them, but not even be able to talk about what the issues/fixes were.

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