Which command displays from which disk the operating system was last booted?

`last` reports user login history and system runlevel changes but does not record or display the boot device.

`bosboot` creates and updates the boot image (BOS boot logical volume) on disk but does not report which device was used for the last boot.

AIX's `getconf` command queries system configuration variables, and `getconf BOOT_DEVICE` specifically returns the device path recorded at the time of the last successful boot. This value is stored in the system configuration database and accurately reflects which disk was used to boot the running kernel.

`bootlist` displays or modifies the ordered list of candidate boot devices configured for future boots, not the device actually used during the last boot.