Specifies the filename of the boot file for the target disk.
Architecture-specific defaults are applied for the boot file. For I64,
the default is SYS$SYSROOT:[SYS$LDR]SYS$EFI.SYS (SYS$EFI).
The boot file must be contiguous. If the target boot file is not
contiguous, use the DCL command COPY/CONTIGUOUS or another functionally
similar mechanism to recreate a contiguous version of the boot file.
The boot file must also be marked NOMOVE (using the DCL command SET
FILE/NOMOVE) to avoid a bootstrap failure that could result from the
normal and expected operations of disk defragmentation tools.