System Initialization and Acceptance Testing (Normal Operation)
4.7 Operating System Bootstrap
4.7.3 Device Dependent Secondary Bootstrap Procedures
The following sections describe the various device dependent boot procedures.
4.7.3.1 Disk and Tape Bootstrap Procedure
The disk and tape bootstrap supports Files–11 lookup (supporting only the
ODS level 2 file structure) or the boot block mechanism (used in PROM boot
also). Of the standard DEC operating systems, OpenVMS and ELN use the
Files–11 bootstrap procedure and Ultrix-32 uses the boot block mechanism.
VMB first attempts a Files–11 lookup, unless the RPB$V_BBLOCK boot
flag is set. If VMB determines that the designated boot disk is a Files–11
volume, it searches the volume for the designated boot program, usually
[SYS0.SYSEXE]SYSBOOT.EXE. However, VMB can request a diagnostic image
or prompt the user for an alternate file specification. If the boot image can’t be
found, VMB fails.
If the volume is not a Files–11 volume or the RPB$V_BBLOCK boot flag was
set, the boot block mechanism proceeds as follows:
1. Read logical block 0 of the selected boot device (this is the boot block).
2. Validate that the contents of the boot block conform to the boot block
format (see below).
3. Use the boot block to find and read in the secondary bootstrap.
4. Transfer control to the secondary bootstrap image, just as for a Files–11
boot.
The format of the boot block must conform to that shown in Figure 4–5.
4–30 System Initialization and Acceptance Testing (Normal Operation)
