Before the kernel is started, the system is controlled by the read-only-memory (ROM) Basic Input/Output System (BIOS), which is the firmware interface on a non-SPARC based system.

Hardware adapters can have an on-board BIOS that displays the physical characteristics of the device and can be used to access the device.

During the startup sequence, the system BIOS checks for the presence of any adapter BIOS, and if found, loads and executes each adapter BIOS. Each individual adapter's BIOS runs self-test diagnostics and displays device information.