5.0beta won't boot on a Dell Dimension 8400

["Steven M. Bellovin" <smb%cs.columbia.edu@localhost>]

I have two almost-identical Dell 8400s.  On one of them, I can't boot a
5.0beta installation CD from the other day -- I get an NMI panic.  (The
exact version doesn't matter; I haven't been able to boot any -current
for a while.) However, 4.99.72 from August 9 runs just fine.  Oddly
enough, the other one has no trouble booting.

If I go into the BIOS and change the disks from AHCI to ATA, however, I
can boot.  The last line printed before the panic is

        ahcisata0 port 0: device present, speed: 1.5Gb/s

which is why I tried changing that option.  The next few lines, on a
working kernel, are

        ahcisata0 port 2: device present, speed: 1.5Gb/s
        ahcisata0 port 1: PHY offline
        ahcisata0 port 3: PHY offline

but disconnecting the second drive and disabling it in the BIOS doesn't
help with the boot process.

I have no idea why the other machine works.  Once I disconnect the
second drive, the only difference is in some USB devices, and according
to the dmesg those are probed after the failure.

If anyone wants, I can post a working dmesg from either machine.  Shall
I send-pr?

                --Steve Bellovin, http://www.cs.columbia.edu/~smb