This feature is new in the Solaris Express 11/04 release.
The Solaris 10 OS has the ability to automatically detect whether your system is 64-bit capable and then boot the appropriate kernel.
Following a new installation of the Solaris 10 software, the boot program automatically loads the 64-bit kernel if it detects your system is 64-bit capable. Otherwise, the program loads the 32-bit kernel.
Following an upgrade installation of the Solaris 10 OS on a system that is configured to load the default 32-bit kernel, the system now automatically determines whether to load the 32-bit or 64-bit kernel. If the system was configured to load a non-default kernel, the system continues to load that non-default kernel. Procedures for customizing a system to load a specific kernel are outlined in Chapter 8, “Shutting Down and Booting a System (Overview)” in System Administration Guide: Basic Administration.
Further documentation about the kernel selection procedure is provided in the Solaris 10 documentation at http://docs.sun.com.