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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:

Load block 0 of the boot device by fiddling with the console keys as appropriate for your hardware. If you have no appropriate ROM, some programs suitable for manual use are given below.
Type boot.
When the prompt is given, type
depending on whether you are loading from an RP04/5/6 or an RP03 respectively. The first 0 indicates the physical unit number; the second indicates the block number of the beginning of the logical file system to be searched. (See below).

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 following

	rp	RP03
	hp	RP04/5/6
	rk	RK05
For 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
	005040		clr	-(r0)	/ rkda cleared by start
	010040		mov	r0,-(r0)
	012740		mov	$5,-(r0)
	105710	1:	tstb	(r0)
	002376		bge	1b
	005007		clr	pc
RP (drive 0)
	012700		mov	$rpmr,r0
	005040		clr	-(r0)
	005040		clr	-(r0)
	005040		clr	-(r0)
	010040		mov	r0,-(r0)
	012740		mov	$5,-(r0)
	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