|BOOT(8)||System Manager's Manual||BOOT(8)|
boot - startup procedures
A PDP11/45 and PDP11/70 UNIX system is started by a two-stage process. The first is a primary bootstrap which is able to read in relatively small stand-alone programs; the second (called boot) is used to read in the system itself.
The primary bootstrap must reside in the otherwise unused block zero of the boot device. It can be read in and started by the standard ROM programs, or if necessary by keying in a small startup routine. This program is capable of loading type 407 executable files (not shared, not separate I&D). The user types on the system console the name of the program wished, in this case boot, followed by a carriage return; the named program is retrieved from the file system that starts at block 0 of drive 0 of the boot device. No prompt is given, no diagnostic results if the file cannot be found, and no provision is made for correcting typographical errors.
The second step, called boot, actually brings in the system. When read into location 0 and executed, boot sets up memory management, relocates itself into high memory, and types a `:' on the console. Then it reads from the console a device specification (see below) followed immediately by a pathname. Boot finds the corresponding file on the given device, loads that file into memory location zero, sets up memory management as required, and calls the program by executing a `trap' instruction. Normal line editing characters can be used.
Conventionally, the name of the secondary boot program is `/boot' and the name of the current version of the system is `/unix'. Then, the recipe is:
When the system is running, it types a `#' prompt. After doing any file system checks and setting the date (date(8)) a multi-user system is brought up by typing an EOT (control-d) in response to the `#' prompt.
Device specifications. A device specification has the following form:
where device is the type of the device to be searched,
unit is the unit number of the device, and offset is the block
offset of the file system on the device. Device is one of the
rp RP03 hp RP04/5/6 rk RK05For example, the specification
indicates an RP03 disk, unit 1, and the file system found starting at block 7000 (cylinder 35).
ROM programs. The following programs to call the primary bootstrap may be installed in read-only memories or manually keyed into main memory. Each program is position-independent but should be placed well above location 0 so it will not be overwritten. Each reads a block from the beginning of a device into core location zero. The octal words constituting the program are listed on the left.
RK (drive 0): 012700 mov $rkda,r0 177412 005040 clr -(r0) / rkda cleared by start 010040 mov r0,-(r0) 012740 mov $5,-(r0) 000005 105710 1: tstb (r0) 002376 bge 1b 005007 clr pc
RP (drive 0) 012700 mov $rpmr,r0 176726 005040 clr -(r0) 005040 clr -(r0) 005040 clr -(r0) 010040 mov r0,-(r0) 012740 mov $5,-(r0) 000005 105710 1: tstb (r0) 002376 bge 1b 005007 clr pc
/unix - system code
/usr/mdec/rpuboot, /usr/mdec/hpuboot - copies of primary bootstrap
/boot - second stage bootstrap