OSX RAM limit?

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werby

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OK people, whats the straight dope on how much ram can be allotted to any given application under Panther?

On the Adobe discussion boards I've read that there is a 2GB limit to any application, even though G5s support up to 8GB of ram. The story is, apparently, that OSX is actually running 32-bit (not 64-bit) and that 64-bit computing is "years" away.

2GB is a limitation of 32-bit computing because:
Quote: "It's a fundamental computer science limit. 2^32 = 4GB, the top bit is usually used to help distinguish system address space from application address space, so applications have 2^31=2GB of address space to work with"

OK, well, not that I understand that, but is this the case with G5s? So apple hypes a "64-bit processor" but the OS (and therefore the apps that run under it) can only run 32-bit? So this is pretty deceptive, right? There's certainly no mention of it on Apple's website or discussion boards.

Plase comment and/or enlighten me!
 

rman


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The current operating system Panther is configured to run only in 32bit mode. So you are half right. Once the applications and OS is compiled to run on 64bits you will see the memory limits raised.

Not all of the current applications can use the G5 64bit processor. Since we don't know what is comming in OS 10.4. It could be 32/64bit enabled. Meaning that if you have a G5 and an application that can make use of the 64 bit processor, it will work fine. Otherwise the system will work at 32bit as usual.
 
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werby

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MacAddikt said:

From the above link on Apple's website, I quote:
"With 8GB of main memory, the PowerMac G5 can hold a gigantic 3D model, a complex scientific simulation or a sequence of HD video entirely in RAM"

This, I think, is misleading. It implies that any given program can access ALL 8GB of ram, which is currently NOT TRUE. I realize with 10.4 and newer software will come this ability, but right now, every app is limited to 2GB, right?

Basically I'm just trying to get a straight answer:
IS THERE A 2GB LIMIT TO HOW MUCH RAM AN APPLICATION CAN ACCESS?
 

rman


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Post that question on the Apple board. You should get the straight answer that you are looking for.
 
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werby

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rman said:
Post that question on the Apple board. You should get the straight answer that you are looking for.

Well, I did, and this is what I got:
"The _machine_ (running in 64 bit mode) is capable of accessing up to 4 TB of RAM, but a process running on MacOSX (which only supports 32bit addressing - 1 bit for user vs. OS address space) can only access 2GB.

In other words, the G5, with its 64bit register file(s) and instruction set certainly supports direct addressing of all 8GB in the machine (up to the VM limit which I've forgotten now). But in order for a process running on an OS running on the G5 to access all 8GB, that OS would have to provide an address _larger_ than 32bits in size and the process would have to be compiled to take advantage of that."

SOOOoooo... there ya have it: 2GB Ram limit. CONFIRMED!
 

rman


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So 2GB wihile running in 32bit mode. If the application were compiled to run 64bit, that would be a different situation.
 
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rman said:
So 2GB wihile running in 32bit mode. If the application were compiled to run 64bit, that would be a different situation.

Well, as I understand it, the application AND the OS both need to run in 64bit mode. Maybe Tiger + Photoshop 9?
 
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It's rather tricky because the G5 isn't truly a 64 bit computer as Apple claims. Parts of the chip are 32 bit, and parts of it are 64 bit. Apple had to do this so that Panther would still run on the G5 without being completely redesigned.

But as you found in your research, 2 GB is the general limit depending on which program you're using. Until Apple develops a real 64 bit processor and OS....this limitation will always be there.
 

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The G5 is a 64bit processor. It also has be desined to run 32bit code. When Apple releases a 64bit OS you will see a difference.
 

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