[nylug-talk] LOWMEM vs. HIGHMEM performance advantage?

[Peter C. Norton]

On Fri, Apr 18, 2008 at 03:52:16PM -0400, Ruben Safir wrote:
> On Fri, Apr 18, 2008 at 08:08:57AM -0700, Peter C. Norton wrote:
> > On Thu, Apr 17, 2008 at 09:02:36PM -0400, Ruben Safir wrote:
> > > Why do we still have this ancient DOS ritual?
> > > 
> > > Ruben
> > 
> > 1) Because the kernel reserved too much address space back when 32mb
> >    was big.
> > 
> > 2) Because PCI is 32-bits, x86 from pentium2 on has bank-switching
> >    capabilities to make it sort-of 36-bits.
> > 
> 
> 
> Can you explain this in more detail, because my understand was that
> GAS assembler essential addresses all ram linearly.

Besides saying that 32 bits < 36 bits, I'm not sure where to go with
it. PCI devices address 32 bits, x86 apps with PAE extensions address
36 bits with some extra help from the kernel.
 
> I'm not sure how these things affect the memory addressing.

There is a 2^32 * 2*4 memory address locations that the CPU can
address that regular PCI devices can't?

-Peter

-- 
The 5 year plan:
In five years we'll make up another plan.
Or just re-use this one.