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Memory

Created by dave. Last edited by dave, 12 years and 361 days ago. Viewed 1,944 times. #3
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Memory Limitations

This is all from memory and probably wrong.

Physical:

ProcessorPhysical Address Limit
32-bit P*4GB
32-bit P* with PAE64GB (limited by mother board)
Note that PAE-accessed memory is slower than the first 4GB of RAM (however it is still hugely faster than disk) and some kernel structures must live in the first 4GB of memory, so you might exhaust this "low" memory before you exhaust all of your RAM.
64-bit CPUeffectively unimited (except by mother board and your ability to pay)

Kernel Process Limits:

CPU TypeProcess Limits
32-bit CPU4GB (1GB kernel/stack; 3GB user use)
There are allegedly some patches out there which can fiddle with this ratio.
64-bit CPUeffectively limited only by RAM/Swap and your ability to pay for memory for your machine

Note that when I say effectively unlimited I mean for PC-class uses. There is no way you are sticking a terabyte of stuff into a PC-class system. Right now I know of Opteron motherboards which can take 32GB of RAM, however none of my current customers have either the requirement for such a machine or the finances to pay for it.

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This is a collection of techical information, much of it learned the hard way. Consider it a lab book or a /info directory. I doubt much of it will be of use to anyone else.

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