The /platform/i86pc/multiboot program is an ELF32 executable that contains a header which is defined in the Multiboot Specification.
The multiboot program is responsible for performing the following tasks:
Interpreting the content of boot archive
Autodetection of systems that are 64-bit capable
Selecting the best kernel mode for booting the system
Assembling core kernel modules in memory
Handing control of the system to the Solaris kernel
After the kernel gains control of the system, the kernel initializes the CPU, memory, and device subsystems. The kernel then mounts the root device, which corresponds to the bootpath and fstype properties that are specified in the /boot/solaris/bootenv.rc file. This file is part of the boot archive. If these properties are not specified in the bootenv.rc file, or on the GRUB command line, the root file system defaults to UFS on /devices/ramdisk:a. The root file system defaults to UFS when you boot the installation miniroot. After the root device is mounted, the kernel initializes the sched and init commands. These commands start the Service Management Facility (SMF) services.