IBM 6C4 - Manual (Page 107)

Multiboot Startup
Multiboot Startup toggles the multiboot startup flag, which controls whether the
multiboot menu is invoked automatically on startup.
Exiting System Management Services
After you have finished using the system management services, type x (for exit) at the
Utilities menu to boot your system or partition. On all other screens, typing x returns
you to the previous screen.
Chapter 4. Using System Management Services 89