RAM question for everyone!

[Jeff Voskamp]

Les wrote:
> On Fri, 2009-01-23 at 11:07 -0500, Mark Haney wrote:

> I guess I do not comprehend the issue of more memory stressing low
>   
> memory?
>
> I know that a 32 bit system is constrained in addressing to something
> like 4G, due to the intel addressing architecture, and 32 bit
> constraint, so applications were developed to go beyond that.  But given
> that the system maps the logical memory to physical memory, and some can
> do this via hardware, how does adding more memory add more stress?  If
> the system is running the application now, the basic change is reducing
> swapping to disk, is it not?
>
> Regards,
> Les H
>   
While the 32bit machine can physically use more then 4G of memory the 
I/O hardware can only move stuff in and out of the first 4G. Therefore 
any I/O that a process in "high" memory is doing has to be 
bounced/buffered through somewhere under the 4G mark.  The CPU ends up 
doing all the copying and the memory is now committed to I/O buffering 
rather than programs or data.

Jeff Voskamp
Feel free to correct me if I'm wrong (and I know you will).