System Startup, Configuration, and Shutdown Reference Manual (32650-90907)

Appendix C
Reading Stable Storage and Nonvolatile Memory
Reading Stable Storage Contents
192
Reading Stable Storage Contents
Stable storage contains the boot path information along with other critical file system parameters in a
minimum area of 96 bytes of high-reliability memory. The storage maintains the critical parameters even if
the storage card is removed from the backplane. After the initial memory controller is initialized, the
processor-dependent code (PDC) accesses stable storage to determine the boot device and console selection
process.
The stable storage contents are allocated as shown in Figure C-1.
Figure C-1 Stable Storage Contents
NOTE Byte addresses are numbered beginning with 0. For example, 0 is the first byte, 1 is the second.
Decimal byte address 0 contains the status of the autoboot and autosearch flags. The byte contains two
hexadecimal values. The first two binary digits of the first value show the flag status as either ON (1) or OFF
(0). Byte 7, obtained by reading decimal address 4, contains the logical module index.