How do I find out my motherboard model?

You can try:

dmidecode -t 2
# dmidecode 3.3
Getting SMBIOS data from sysfs.
SMBIOS 2.6 present.

Handle 0x0200, DMI type 2, 9 bytes
Base Board Information
        Manufacturer: Dell Inc.
        Product Name: 01V648
        Version: A06

Or

root@nfs2:/# lshw | more
nfs2
    description: Rack Mount Chassis
    product: PowerEdge R410
    vendor: Dell Inc.
    serial: 1SD07V1
    width: 64 bits
    capabilities: smbios-2.6 dmi-2.6 smp vsyscall32
    configuration: boot=normal chassis=rackmount uuid=44454C4C-5300-1044-8030-B1C04F375631
  *-core
       description: Motherboard
       product: 01V648
       vendor: Dell Inc.
       physical id: 0
       version: A06