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[DieHard]

In the past... it was noted that certain applications get buggy when system has more than 1 gigabyte of physical RAM under OS 9.

Also, Web and print references will vary... some will state that Mac OS 9 can address to 2 GB of RAM, while others say the 1.5 GB limit is the maximum. 

I decided to create this thread to gather user experiences with Mac OS 9 applications and RAM limits; also to wipe the slate clean and try some real world testing and the explore Mac OS 9 system limits.

So let's begin...

We will use an Powermac G4 MDD as the test unit since it has 4 slots and we will start with 3 out of 4 filled (512MB X 3) for a total of 1.5GB

No Shocker here... Built-in Memory (or Physical Memory) is 1.5 GB and finder shows Memory used per application and the System itself using 68.1MB, Also the largest unused Block (of available memory) is 1.41GB

Now for test 1: We create the maximum RAM disk allowed (and tell it to re-create on Boot up) of 256 MB and re-start



Hmmm... pretty interesting, but expected... Built-in Memory (or Physical Memory) is 1.5 GB and finder shows Memory used per application and the System itself using 314.8MB instead of 68.1MB (this is obviously the overhead of the RAM disk itself and shows an increase of 246.7MB (not 256MB), But now the largest unused Block (of available memory) decreases down to 1.17 GB (a .24 GB Difference.... off by .1 since a 256 MB RAM Disk should be .25 GB)
We can conclude that although the numbers are not 100%, the small deviation is acceptable and that a RAM disk will decrease the available memory and proportionately add itself into the Mac OS category as far as Memory used.

OK so let's go for broke... now we have 4 out of 4 filled (512MB X 4) for a total of 2 GB, we expect from all printed material that the system cannot go past 1.5 GB

OMG the system sees it ! (or does it)... Built-in Memory (or Physical Memory) is 1.99 GB !!

Finder shows Memory used per application and the System itself using 564.9 MB (What the F%$k), Also the largest unused Block (of available memory) is 1.42 GB.... wait a minute we add 512MB and we only get .01 GB more in available memory (from 1.41 to 1.42) and the OS itself is now bloated from 68.1MB to 564.9 MB (496.8 MB increase) ??!!

We can theorize that the ceiling is actually 1.5 GB (or maybe 1.6 GB since we now have 1.42 GB unused) and we can assume that it does not know what to do with the extra 512MB so it adds it to the Mac OS category as used by the system itself and it like a dead fish or more like a wasted layer of resources that we cannot get to

Wait... Maybe we can use it as a RAM Disk ? at least grab back 256 MB...

Now for test 2: We create the maximum RAM disk allowed (and tell it to re-create on Boot up) of 256 MB and re-start



Hmmm... this sucks, just as bad as before... yet kinda interesting... Built-in Memory (or Physical Memory) is 1.99 GB and finder shows Memory used per application and the System itself using 811.9 MB instead of 68.1MB !!! (this is obviously the overhead of the RAM disk and the wasted 512MB); Mactron would have a nervous breakdown if he saw his System use 811.9 MB (he gets upset if he wastes 1 MB), Now the largest unused Block (of available memory) decreases down to 1.18 GB (the worst number yet).

Again, we can conclude that although the numbers are not 100%, a RAM disk will decrease the available memory and proportionately add itself into the Mac OS category as far as Memory used. Also, the idea of trying to load the RAM disk into the unused area between (1.5 GB to 2 GB) and reclaiming some of the wasted RAM above 1.5 GB was a bust. Until,  the Mac OS 9.4 Update is released (that may take a while), we are stuck with a 1.5GB physical memory limit in OS 9.2.2 as far as the OS is concerned.

NEXT... Please post your experiences of application limits/issues here...

[Protools5LEGuy]

We will use an Powermac G4 MDD as the test unit since it has 4 slots and we will start with 3 out of 4 filled (512MB X 3) for a total of 1.5GB

You are pro Mono vs Duals. I have a MDD Dual 866 with 2 gigs installed of Kingstom DDR-400, Asus Gforce 2MX Twin (Only VGA output) with an Audiomedia III.

I will try to mimic your install and make your tests on my machine if that could help anyway. It could also compare CPU, Dual vs Mono and bandwith as my bus will run 133 and my mem 266.

[IIO]

Wait... Maybe we can use it as a RAM Disk ?

lol^^

[DieHard]

Wait... Maybe we can use it as a RAM Disk ?

lol^^

Guess you been there

[MacTron]

The Mac Os 9 can address up to 4GB of memory. But due to memory map structure, up to 1.5 GB can be RAM, the remaining can be ROM or what ever. This 1.5 GB limit could be enough at its time ... but now a days...
If More than 1.5 GB of RAM is present in the machine, only 1.5 is usable as RAM, the remaining appears as used by the Mac Os, who knows in which way ... LOL

So we only have to change the memory map where it puts 1.5 we shall put 2 o 3 GB... LOL

[jt]

WAG: dunno really, but I think I've seen this kind of thing before. It sounds like the messy move from 24bit to 32bit addressing to me, extra stuff gets stuffed into System Allocations?

If 7 went 32bit only and X went (sort of) 64bit only it could be the same behavior. However Apple had plenty of development time  .  .  . 

.  .  .  between the incredibly buggy 9.0 release and the even more incredibly late and bug-ridden  X.0 release to have cleaned up their long jump technique or it was simply easier to compartmentalize a 32bit space under NetBSD than 24bits inside a 32bit container? No a 'Nix jockey here so its still just a WAG.

Possible answer: Apple borked OS9's System Reporting on the jagged journey to higher memory address spaces?  OS9 gots no 64bit reverse memory addressing control panel kluge = GOOFY MemStats?

Nah! Couldn't happen.

I really hope your Mileage Does Vary on this.

[jt]

So we only have to change the memory map where it puts 1.5 we shall put 2 o 3 GB... LOL

Heh! You beat me to it by 5 minutes, I need to type faster. Very succinctly put, it'll probably be a lot easier to hack memory reporting to work correctly. 

[IIO]

So we only have to change the memory map where it puts 1.5 we shall put 2 o 3 GB... LOL

and after that we should hexedit our processor speeds and the number of cores.

or what about a system suitcase patch which makes the computer produce instead of consume electricity?

[Protools5LEGuy]

There's precedent for gaining access to that disappearing half Meg of RAM. Connectix developed Compact Virtual to get around such ROM based memory addressing limitations.  At the dawn time NuBus architecture PMMU operations were moved on die for the 68030 and Accelerators for the 4MB limited 68000 Compacts became available. Some were equipped RAM SIMM slots implementing Silicon Disk/Virtual Memory capabilities up to 8x the MoBo's 4 on the floor.

The effort needed to develop such capabilities for the 33% increase available on the floor of the PowerMacs G4 under OS9 may or may not be a worthwhile endeavor. But doing it would certainly be cool as hell!

Quote from: MacTron on December 10, 2014, 11:44:39 AM

    The Mac Os 9 can address up to 4GB of memory. But due to memory map structure, up to 1.5 GB can be RAM, the remaining can be ROM or what ever. This 1.5 GB limit could be enough at its time ... but now a days...
    If More than 1.5 GB of RAM is present in the machine, only 1.5 is usable as RAM, the remaining appears as used by the Mac Os, who knows in which way ... LOL

ROM in RAM? How to make the G4 "feel" the RAM as ROM? Finder and other could take advantage of the 0.5 gig RAM left if we told the system to behave that as ROM? You all are joking or talking seriously?

Please folks, back to topic

[Knezzen]

ROM = Read Only Memory
RAM = Random Access Memory

He is talking about using it as a ROM, putting something in it and use it for fast reading.
Not putting the Mac OS ROM in there. Just to clarify

[IIO]

but his question is eligible: somehow it does not make sense that it is available as ROM, because you have no chance to get something non-OS9 onto a memory chip while MacOS9 is running.

about the reason, that is probably more difficult than one might think.

in a 32 bit OSX one process can use 4 GB, because that is about what you get with a 32 bit adress space. as you might know, in a 32 bit windows app you´ll only be able to half of that, because the adress space is shared between the RAM adresses and other things.

in windows for example, the adress room has to be shared with the graphics card, the onboard controllers, and even the ROM.

in theory it should be possible for the OS itself to use more than 1.5 gb: MacOS and the apple hardware is fully 32 bit since around Mac OS 7 times.

on MacOS9 ... i dont really know it ... but i could imagine that the limit has something to do with the PCI slots. there are windows laptops, too, where you can only use 1.5 gb of RAM.

afaik you can not even use bigger dimms with a G4 for OSX, because the slots will always only see the first 512 mb. this is another example of limitation by design.

when i remember right, that funny MacOS 8 for x86 could also only use 1.0 gb.

[jt]

Quick post pre-work:

first: I'm looking for Developer Notes on the 4 DIMM g4s. Does anybody have links handy?

second: while searching, I found parallel discussion from five years ago, much good information on first page re 3/4 DIMM configurations and even why(?), haven't followed it further as yet:

G4 Macintosh - what is located at Real Address 0x80000000 ?

The "ROM" available at the top of the  4MB  address space in New World Macs

My focus has been on the NuBus Architecture, but the folks involved in that pursuit and the pre-Slot Manager 68000 Architecture have been hard at work filling unused ROM mapped address capacity with things useful in hardware ROM. They're the folks to ask questions about loading that half Meg of FLASH with something useful before the OS loads. Wicked smart creative folks in that world of development there that's probably directly applicable to the Universal 9.2.2 Installer, much easier than burning physical ROMs to fit on custom ROM SIMMs and Conversion Boards.

https://mac68k.info/forums/index.jspa?categoryID=1

I'd posted info on Connectix' Compact Virtual that disappeared. Supported DIMM sizes may or may not be addressable as VRAM with a similar System Hack, dunno. Old World memory sizes Apple supported and higher capacity SIMMs that became avaiable eith the development of higher density packages were distinctly d1fferent in many cases.

No shipping version of any Mac OS can address higher than 512MB DIMMs, but that doesn't necessarily mean the addressing hardware in non-existant, it may be addressable as Silicon Disk VRAM per the Compact Virtual route. The folks at Mac68k would be the ones to ask. I'm off to work while you folks have the day off, but I can at least watch developments there. 

[DieHard]

This page is also helpful... G4 Models

General information regarding the type of memory, number of memory slots, RAM speed, and Max RAM supported

http://www.everymac.com/systems/apple/powermac_g4/faq/power-mac-g4-how-to-install-memory-ram-max-capacity-os9-osx.html

[Texas_RangerAT]

WAG: dunno really, but I think I've seen this kind of thing before. It sounds like the messy move from 24bit to 32bit addressing to me, extra stuff gets stuffed into System Allocations?

Yup, me too! I think the "About this Macintosh" memory info section behaved the same if you installed a pre-7 system on any Mac II with more than I don't know how many MB of RAM - the Finder suddenly got bloated way out of proportion to sort of fill up the gap between the system's memory limit and the actual memory size. I can't for my dear life remember what that ceiling was but I definitely tried 6.0.3 on a IIci with 32 MB and got that phenomenon. Or maybe it was a IIcx with 16 MB and I tried it with and without a 32-bit enabler. So I suspect this has something to do with bodged-up memory addressing.