On 4/29/02 at 10:53 AM, nathanw@wasabisystems.com (Nathan J. Williams) wrote:

> Michael Core <520079546242-0001@t-online.de> writes:
> 
> > > You'll only be able to use 4G with NetBSD, to my knowledge.
> > > BTW, how does 8G work with a PRo ? I though only xeon could handle
> > > more than 4G RAM.
> > 
> > IIRC the Pentium Pro has a 36-bit address bus but I thought it was only
> > useful to handle upto 64GB swap space.
> 
> The trick is that only the *physical* address space is expanded to 36
> bits; the virtual address space is still 32 bits. In principle, this
> means that you could have, say, 32 processes, each using 2G of memory,
> all resident, without swapping. But no single address space can access
> more than 4G at a time. This includes the kernel's address space, so
> managing this pile of memory requires some cleverness.
> 
>         - Nathan


Pentium Pro
    
36-bit
    
65,536 MB
of total memory to be access, 
unisys system had full access of memory.



<snip>

As early as June 1991, Intel circulated confidential documents describing the
new features of their P5 processor, eventually known as the "Pentium Processor."
Most of those new features would be shrouded in controversy, their details kept
secret by Intel. But one of the most advanced features-Physical Address
Extensions (PAE)-was entirely removed. PAE gave the processor the ability to
address up to 64 GB of physical memory (36-bit address bus), and access page
sizes of 2 MB. The larger physical-address space and the new 2-MB paging
features were interrelated, as both were enabled by the same control bit. In all
other operating modes, the normal 32-bit address space was in operation. 

__

Rick