[CentOS] Why noapic acpi=off on new Centos 4.6 system?

I just installed CentOS 4.6 (because I had 4.6 media handy) on a new
system, which has a SuperMicro PDSMi mobo with an E4600 CPU.

I then did yum update to get to 4.7, although I don't think that's
relevant to my query.

I wondered why "shutdown -h" would not power down the system. I then
also discovered that the soft power button did not initiate a switch
to runlevel 0 to do a controlled shutdown.

When I looked in grub.conf, I discovered that the installer had included
the boot parameters "noapic acpi=off". I removed them and rebooted, and
then found that both soft shutdown from the power button and the final
poweroff worked fine. I haven't stressed the system yet, but it seems
to boot and run fine.

My question is (at last): why did the installer decide it necessary to
include "noapic acpi=off"? Previous installs of CentOS on other hardware
have not done that.

Cheers
Tony
-- 
Tony Mountifield
Work: tony at softins.co.uk - http://www.softins.co.uk
Play: tony at mountifield.org - http://tony.mountifield.org