i386 with PAE or AMD64 on PowerEdge with 4G RAM

[Jeremy Chadwick]

On Mon, Jun 18, 2007 at 05:15:30PM -0400, Martin Turgeon wrote:
>  My setup is fairly standard (as I described), should I expect problem with
>  64 bit version of these programs?

Like I said, I don't run 64-bit OSes because I prefer compatibility.
Believe me, the instant you run into some quirky problem with either the
kernel or any of its subsystems, or a third-party program (from ports or
otherwise), the first thing you'll be told is "it works for me on i386,
have you tried i386?"

I'm sorry if this sounds condescending or combative, but it's what I
continually see on other lists.

>  You'll lose the amount of RAM you're seeing due to PAE addressing for
> > PCI address space.  I can dig you up a usage map (broken down by how
> > much is taken up by each portion; PCI, ACPI, etc.) if you want one.
> > It's for SuperMicro systems, but the general idea applies to most
> > everything.
> 
>  I'm not sure to understand what you mean by that. Are you saying that PAE
>  will eat the 500M that should be available?

PCI addressing is actually responsible for most of it, but it's worse
when PAE is in use.  This is one of the many reasons a lot of people
prefer to run in 64-bit environments.  Taken from a Supermicro
motherboard manual, documenting the issue (seems their math may be off
by 2MB ;) ):

http://www.supermicro.com/manuals/motherboard/3000/MNL-0889.pdf

4. Due to memory allocation to system devices, memory remaining
available for operational use will be reduced when 4 GB of RAM is used.
The reduction in memory availability is disproportional. (Refer to the
following Memory Availability Table for details.)

System Device                   Size      Physical Memory
                                          Remaining (-Available)
                                          (4GB Total System Memory)
===================================================================
Firmware Hub flash memory       1MB       3.99GB
  (System BIOS)
Local APIC                      4KB       3.99GB
Area Reserved for chipset       2MB       3.99GB
I/O APIC (4 Kbytes)             4KB       3.99GB
PCI Enumeration Area 1          256MB     3.76GB
PCI Express (256 MB)            256MB     3.51GB
PCI Enumeration Area 2          512MB     3.01GB
  (if needed)
  -Aligned on 256-MB boundary-
VGA Memory                      16MB      2.85GB
TSEG                            1MB       2.84GB
-------------------------------------------------------------------
Memory available to OS and                2.84GB
  other applications
===================================================================

-- 
| Jeremy Chadwick                                    jdc at parodius.com |
| Parodius Networking                           http://www.parodius.com/ |
| UNIX Systems Administrator                      Mountain View, CA, USA |
| Making life hard for others since 1977.                  PGP: 4BD6C0CB |