what is the difference between swap partition and swap

Jonas Norlander jonorland at gmail.com
Fri Mar 13 12:21:55 GMT 2009


2009/3/13 Derek Broughton <derek at pointerstop.ca>:
> Jonas Norlander wrote:
>
>> 2009/3/12 Derek Broughton <derek at pointerstop.ca>:
>>> Brian Norman Wootton wrote:
>>>
>>>> There used to be a maximum partition size for swap of 2 GB, I don't know
>>>> if this still applies.
>>>
>>> Never in my memory (I started using at least 3GB when I bought my Dell
>>> laptop at least 5 years ago, because I was using swap for tmpfs).
>>
>> Well there are a limit of 4 Gb (if you use 32 bit architectures) for
>> your virtual memory and that includes RAM, Swap, Graphics memory and
>> other devices.
>
> Surely that's not right.  People are using 4GB _real_ memory (using PAE
> kernels) - do they not get any swap at all?

Processors from Pentium Pro and above have PAE and that gives you a
limit of 64 GiB of Virtual Memory so probably all modern CPU and OS
can have large swap space.
I was mixing things up, was think more of how much memory a process
could access and was not really follow the OT.

PAE is one way to access more memory where the physical address size
is increased from 32 bits to 36 bits giving you a total of 64 GiB but
you still got a limit of 4 GiB Virtual address space per process. But
there are ways that the OS can handle that.
<snip from wikipedia>
For application software which needs access to more than 4 GB of RAM,
some special mechanism may be provided by the operating system in
addition to the regular PAE support. On Microsoft Windows this
mechanism is called Address Windowing Extensions, while on Unix-like
systems a variety of techniques are used, such as using mmap() to map
regions of a file into and out of the address space as needed.
<snip>


/ Jonas



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