[GLLUG] General Question

[Charles Ulrich]

On 2012-09-06 15:38, J Neveau wrote:
> This is always a great question.  There seems to be a lot of
> confusion about total memory usage in Windows, Linux, etc.
>
> Additionally, the factor of 32bit and 64bit OS comes into play.  I've
> seen people bragging about their 64bit processors, while
> running a 32bit operating system.  It's like giving a man in a row
> boat two oars for paddling and only one oar lock for the boat. 

In this case, I take "older laptop" to mean one with a 32-bit CPU, 
although this is not always a safe assumption anymore.

The performance difference between a 32-bit and 64-bit OS on a 64-bit 
CPU is present and statistically significant, but nothing the average 
user is likely to notice. The bigger difference is the memory handling, 
which you talk about below.

> This is my understanding; someone correct me if there's an error.
>
> Any 32-bit operating system can only address 2^32 bits of RAM, which
> is 4GB. Since PCI devices are memory mapped, any RAM that they use
> needs to be part of the address space that the OS references. If you
> use 4GB of RAM, this will mean that the memory from your PCI devices
> will therefore "overlay" a portion of your RAM and cause less RAM to
> be visible to your OS. 
>
> For example, if you have two 512MB video cards in SLI mode, you will
> only be able to see a total of 3GB of ram. 

Newer releases of 32-bit Linux distros tend to ship with a PAE kernel 
by default, which allows Linux to access up to 64GB of RAM. Processes 
are still limited to no more than 4GB, though.

None of this is very relevant to Troy, though, who was contemplating a 
maximum of 2GB of RAM in the machine...

Charles