4 GB Of RAM In A PowerMac G4 MDD?

[CC_333]

Hi,

I am going to receive a 2003 model MDD in the mail soon, and I was wondering about memory capacity.

Since there exists 1 GB DDR RAM modules which are of the correct speed so that they'd be compatible, why couldn't one use them to their full capacity in the MDD?

For some reason, the maximum is listed as only being 2 GB (with each of the four slots filled with a 512 MB module). Is this due to an arbitrary software/firmware limitation which could be circumvented, or is the hardware truly incapable of handling that much memory?

Has anybody tried this? What were your results?

Thank you,

c

 

[uniserver]

i have a mdd as well,

looks like you can go to 2gb ram only but MACOS9 will only see 1500mb, You would have to install osx to get that extra 512mb,

looks like you can use 1gb DDR sticks though,

they were saying its a limitation of the memory controller.

on apple support forum.

i have some 512 sticks , looks like i can just install (3) 512's and be set.

i got os 9.22 on mine, but i miss OSX a tad bit , i need to install a second hard drive in that.

 

[CC_333]

Hi,

I wonder if the memory controller is hackable to support 4 GB?

I don't want to make a huge project out of this; it was just curiosity.

2 GB is plenty most of the time.

c

 

[Dennis Nedry]

This seems like a 32-bit limitation. The maximum addressable memory with 32 bits is 4 GB, and it seems that you could not have a full 4 GB of RAM because some address space must be reserved for other things, such as ROM and peripherals.

For 4+ GB of RAM, you generally have to look at computers that have 64-bit processors. This started with the G5 on Macs.

 

[LCGuy]

My guess is that they would work, but the Mac may only see them as 512MB modules. I once had a Compaq P4 laptop that I tried a 1GB SO-DIMM in - it worked fine, but it only recognised the first 512MB.

 

[jongleur]

Physically, they will work, but the Mac will only "see" 512MB on each. I would have liked to have replaced the 3x512MB SIMMs in my QS2002, but 1.5GB is as much RAM as my ol' work horse can handle.

 

[Dennis Nedry]

What would happen if you put 2x 1GB sticks in there, would you get 2GB, or would each stick be limited to 512MB, so you'd get only 1GB?

I don't know about you but I'm holding out for memristor technology to take off.

 

[LCGuy]

I'd imagine you'd still only get 1GB - I'd be willing to bet that the memory controller can probably only see 512MB per module.

 

[trag]

I read in a forum somewhere of a fellow who was able to install two 1GB DIMMs in an MDD and have it recognized as 2GB of RAM. Additional sticks did not get him any additional capacity. As someone wrote earlier, that's probably a memory map limitation.

It would probably depend on the DIMMs and what kind of memory chips they are made out of. The limitation is usually the row and column addresses. Usually, later memory chips have higher capacities and DIMMs made out of these chips use more row and/or column address lines and often the older machines don't have physical support for the extra line(s).

 

[uniserver]

yeah that is what i saw too,

you can install (2) 1gb sticks, but only OSX will allow you to see and use all 2gb of ram, in MacOS9 it will still work but you will only see and use 1.5gigs, the other 512mb is ignored, kind of like installing 12mb ram in a LCII, the other 2mb are ignored.

 

[BGoins12]

I read in a forum somewhere of a fellow who was able to install two 1GB DIMMs in an MDD and have it recognized as 2GB of RAM. Additional sticks did not get him any additional capacity. As someone wrote earlier, that's probably a memory map limitation.
It would probably depend on the DIMMs and what kind of memory chips they are made out of. The limitation is usually the row and column addresses. Usually, later memory chips have higher capacities and DIMMs made out of these chips use more row and/or column address lines and often the older machines don't have physical support for the extra line(s).

That was probably me. I currently have 2 x 1GB modules in my MDD, and they do show up as 1GB a piece. I tried multiple combinations of modules and it refused to show more than 2GB.

 

[jongleur]

That was probably me. I currently have 2 x 1GB modules in my MDD, and they do show up as 1GB a piece. I tried multiple combinations of modules and it refused to show more than 2GB.

That's handy to know if you get a MDD that's not packed with 4x512MB, and you want to max the RAM - unfortunately my QS only counts the first 512MB on the SIMM.

 

[protocol7]

When I got my first B&W G3 it had 1GB of RAM (4x256) installed, but only 512MB was showing up. When I put the same sticks into my G4 Gigabit Ethernet all 1GB showed up.

Maybe RAM density is playing a part here. I've been working with PCs for years but only came across density recently when upgrading a friend's PC. It had a crappy Foxconn mobo and wouldn't boot with the original pair of RAM sticks I got for it. If I put in one new stick and one old one it would boot but only half of the new stick was recognised. After some google-fu I discovered that some chipsets require low-density RAM. In other words more chips per stick. In this case, with 1GB sticks I needed chips on both sides.

 

[Bolle]

Be sure to not put the 1GB sticks into memory slots that are located next to each other. The Slots in the MDD seem to be kind of paired in groups of two with each group supporting 1GB of memory in total. Sticking 2x1GB into the first two slots will result in 2x512MB showing up while filling only slot 1 & 3 or 2 & 4 at the same time will give you the full 2GB (1.5 in OS 9)

 

[techfury90]

Its not the memory controller. OS 9 has an address space limit at either 1 or 1.5 GB (I forget which, off-hand). OS X supports larger amounts...

 

[ClassicHasClass]

OS 9 is 1.5MB.

 

[Dennis Nedry]

It is perfectly valid to speculate that the 2GB limit is not directly a memory controller limitation, but nothing is proven by the fact that OS 9 and OS X have different limits.

With any sort of complicated digital device, there are often multiple limiting factors. It stands to reason that the memory controller itself can not go higher than 2GB by design due to limited address space on a 32-bit system. Mac OS X may be able to take full advantage of this 2GB while Mac OS 9 has a separate, additional limitation that holds it back to even less than 2GB.

If it isn't a memory controller limitation, then it's a Mac OS X limitation. You could try installing >2GB RAM and then running linux to see if more RAM appears through the OS. You will never get a full 4 GB of RAM on any 32-bit computer though.

 

[Gorgonops]

I suppose it's nitpicky to point this out, but most higher-end 32 bit x86 cpus since the Pentium Pro directly support up to 64GB of RAM (assuming you could find/build a suitable motherboard). Using more than 4GB of RAM for a single process involves resorting to oddball memory models but PAE demonstrates it's certainly *possible* to have more than 4GB of RAM in a 32 bit machine.

(16 bit Superminis from the 1970's, like the larger versions of the PDP-11 that UNIX was developed on, usually had "similar" address space extensions and programming models to allow the direct utilization of RAM sizes greater than the 64k their word length would imply. The segmentation model used in the original Intel 8086 is another, albeit slightly brain-damaged, example.)

Of course, this has absolutely nothing to do with a Powermac G4, since so far as I know 32 bit PPCs have nothing analogous to PAE...

 

[Dennis Nedry]

Some old microcontrollers have very limited RAM addressing so they page around to different chunks of RAM. Is this a similar concept? It seems confusing and top-heavy to address RAM this way.