[EdLUG] How to tell if a computer is 32 bit or 64 bit

Edinburgh Linux Users Group edlug at lists.edlug.org.uk
Sat Jul 30 17:34:06 UTC 2016


On 2016.07.30 03:46, Edinburgh Linux Users Group wrote:
> Hi, thanks to everyone who replied.  I just learned that one needs to
> have
> 4 GB of RAM to take advantage of 64 bit GNU-Linux, so I am out of
> luck, as
> this machine only has 3 GB of RAM.  Is that true, am I out of luck?
> 
> On Fri, Jul 29, 2016 at 11:08 AM, Edinburgh Linux Users Group <
> edlug at lists.edlug.org.uk> wrote:
> 

> Christian Einfeldt

Christian,

That's a bit simplistic.  A 32 bit address can describe at most 4G, unique addresses.
Some of that is address space is take up by the kernel and some by memory mapped IO.
Expect to have about 2G of physical RAM for applications.

Even though you only have about 2G of physical RAM for applications, due to the way virtual memory works in linux, each application can appear to have about 3G of address space in 32 bit mode.  Its a really bad idea not to include the kernel in the address space at all times.
That means that you really can run programs that are too big for physical RAM ... slowly. 

When you go to 64 bit, there are other advantages besides the bigger virtual address space.
You have the use of extra CPU registers that do not exist on 32 bit CPUs. This is a speed improvement.
Memory access may be faster.
if you have an early Intel 64 bit chipset, the wasted (in 32 bit mode) RAM gets mapped above the 4G boundary where it can be used in 64 bit mode.
Early Intel 64 bit chipsets only let you use just less than 3G RAM in 32 bit mode.

The 32 bit/64 bit break even in terms of RAM size is between 1G and 2G.
With 1G RAW or less, use a 32 bit install.  With 2G or more, a 64 bit install.
As has already been said, a 64 bit multilib install gives you the best of both worlds.

Regards,

Roy Bamford





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