Sun Microsystems 220R - Manual (Page 277)

C.1.16 Standard System Facilities
In addition to the previously listed features, the system unit provides the following:
4 TOD/NVRAM for clock and identification functions
4 Flash PROM for operating system initialization. The flash PROM is
re-programmable through UNIX and OBP utilities.
C.1.17 Main Logic Board
The following figure illustrates a block diagram of the system’s main logic board.
Functional Description 277