Mailinglist Archive: opensuse (3605 mails)

[James Knott <james.knott@xxxxxxxxxx>]

Per Jessen wrote:
> Randall R Schulz wrote:
> 
>>> AFAIK, it's the address space size that is 4Gb, not the physical RAM
>>> limit.  Intel Pentium 32bit processors since around the PentiumPro
>>> have all had 36 address lines, so max 64Gb physical memory.
>>> For instance, I have a 32bit Compaq machine that is quite happy
>>> with its 5Gb physical RAM.
>> Ah. I wasn't aware of that. Does Linux allow full exploitation of the
>> memory management hardware of those processors so as to use the full
>> 36 bits / 64 GB of RAM? Presumably it does.
> 
> There is a config option that enables the use of PAE (Physical Address
> Extension - CONFIG_HIGHMEM64G.  AFAIK, that's all you need.  
> 
>> And this is all x86 processors more including and since the first
>> PentiumPro?
> 
> I'm not sure, but at least all Pentium Pro, -II, -III and -4 models.
> 
> http://en.wikipedia.org/wiki/Physical_Address_Extension

That's sort of thing has been around for years and is known as memory
mapping.  For example, many of the old mini-computers used it and there
was even an a version of the Zilog Z80 (Z800?) that used it.  However,
it imposes a performance penalty and applications have to know how to
use it, to gain any benefit.


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