[CentOS] i386 or x86_64 installation

[John R Pierce]

Peter Kjellstrom wrote:
> On Monday 22 January 2007 17:05, Matt wrote:
>   
>> What are advantages of 64 bit OS anyway?  I was thinking with i386 the
>> max RAM you could have was like 4 gigabyte or something?  64 bit
>> allows quite a bit more, right?
>>     
>
> You can have alot of RAM even in a 32-bit system. However, there is also the 
> issue of efficiency and applications being able to actually use alot of 
> memory. Here are some random bits of information on the subject:
>
> * you can have alot more than 4G on 32-bit with pae (hugemem kernels)
>   


PAE is something of a performance hit in the hardware.

without PAE, most newer architecuture boxes running 32bit will be 
restricted to 3GB or 3.25GB addressable physical ram, as the top 1GB or 
750MB or so is needed for the PCI/PCI-X/PCI-E IO addressing spaces (much 
like how the original IBM PC 'realmode' systems could only have 640kB 
and not the theoretical 1MB 8086 addressable memory)

in 32bit, no user process can have more than about 2GB of application 
address space, with addresses > 2GB belonging to the shared kernel 
address space.


 From where I'm sitting, the mainstream applications that benefits the 
most from the large address space of 64bit mode are big database servers.