multiboot —
procedure for booting NetBSD/x86 from a Multiboot-compliant boot
  loader
Multiboot is a specification that defines a protocol between a boot loader and a
  kernel. This protocol allows passing boot information between the two in a
  standard way, allowing any Multiboot-compliant boot loader to boot any
  Multiboot-compliant kernel. The NetBSD kernel supports
  Multiboot if it was compiled with options MULTIBOOT
  (the default in the ‘GENERIC’ and ‘GENERIC_LAPTOP’
  configurations).
Unlike when using the native boot loader, the
    NetBSD kernel recognizes a set of command line
    arguments if booted through a Multiboot-compliant boot loader. This is
    because the Multiboot protocol is not complete enough to completely
    configure a NetBSD kernel.
The following arguments are recognized:
  - console
- Specifies the console device name. Can be one of ‘com’ or
      ‘pc’. If the former, console_addr and
      console_speed should be given too.
- console_addr
- Specifies the serial port address for the console. Defaults to the value
      of options CONADDRor ‘0x3f8’ if
      this was not given.
- console_speed
- Specifies the serial port speed for the console. Defaults to the value of
      options CONSPEEDor ‘9600’ if this
      was not given.
- root
- Specifies the name of the device to be mounted as the root partition. It
      should not be needed because the kernel tries its best to guess which is
      the root partition (basing the decision on the device from which the
      kernel was loaded from). In cases where the automatic detection fails,
      this flag comes useful. Example: ‘root=wd0e’.
GRUB Legacy is the most popular bootloader that supports Multiboot. You can boot
  a NetBSD kernel (assuming it is compiled with
  Multiboot support) with a line similar to the following one:
kernel (fd0)/netbsd.gz -c console=pc root=wd0e
 
multiboot support first appeared in
  NetBSD 4.0.