Subject: Re: MPBIOS vs MPACPI with Intel 7505 chipset
To: John R. Shannon <>
From: Frank van der Linden <>
List: current-users
Date: 10/28/2003 18:05:19
On Tue, Oct 28, 2003 at 10:02:09AM -0700, John R. Shannon wrote:
> Am I better using MPBIOS or MPACPI to configure CPUs and APICs on a 
> motherboard that uses the Intel 7505 chipset? If I experiment, and they both 
> appear to work, what should I look for?

Here are the differences:

MPBIOS (NetBSD code to use the MPS structures):
	* Older method of finding CPUs, I/O APICs, and interrupt routing.
	  Still supported by most (if not all) boards. Should not find
	  virtual CPUs (for the HyperThreading case), although on some
	  boards it does, since the BIOS manufacturer generates a table
	  with them present. Since it's been around for a while, the
	  MPBIOS info is usually reliable. But, there are exceptions,
	  and now that ACPI is becoming the blessed method, BIOS
	  writers may let it bitrot.

MPACPI (NetBSD code to use ACPI info):
	* Newer method of finding CPUs, I/O APICs, and interrupt routing.
	  Supported by newer boards (starting several years ago). Should
	  find virtual CPUs every time (in the HyperThreading case).
	  There are more quirky ACPI than MPS implentations out there,
	  so chances are a bit larger that it'll get things wrong.
	  Also needs all ACPI code to be included in the kernel, which
	  bloats it (though on an MP machine, you're usually not going
	  to care much).

You can just specify them both. MPACPI will be tried first, and if it
fails early, it'll fall back to MPBIOS.

There aren't any runtime advantages that one has over the other once
your kernel is up and running, provided that both work correctly.

- Frank

Frank van der Linden                                  
NetBSD. Free, Unix-like OS. > 45 different platforms.