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Re: Theoretical limit to memory allocation

Subject: Re: Theoretical limit to memory allocation
From: Chris Kane <email@hidden>
Date: Tue, 2 Oct 2001 15:16:55 -0700

On Tuesday, October 2, 2001, at 09:01 AM, Erik M. Buck wrote:

Is the following statement true ?

On Mac OS-X, the theoretical limit to the amount of memory that can be
allocated by one application is approximately 2 Gigabytes.

I just want to check my facts.

The theoretical limit would be 4GB minus a few bytes on PowerPC, on Darwin/Intel I think it might be 3GB minus a few.

However, the practical limit is lower, and depends on whether you mean in many allocations, or in one big allocation (I think the former). In one big allocation, the limit is about 1GB, since the VM space is so fragmented with stuff scattered about.

In the many allocations case, the theoretical limit has to be reduced by the quantity of call stacks, the sizes of libraries, other binaries in memory, and the executable, and, again depending on what you mean, the amount of memory used by system libraries. But that all tends to be less than .75 GB.

Chris Kane
Cocoa Frameworks, Apple

References:
	>Theoretical limit to memory allocation (From: "Erik M. Buck" <email@hidden>)

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