On May 31, 4:45, John Allain wrote: I've lost the context that prompted that particualr question, but if you're asking if a bootstrap always needs 30+ lines of instructions, no, some are much shorter than that. This is the bootstrap for a TU10 magtape: 100000 012700 MOV #0172526, R0 ; TM11 (TU10) MTCMA magtape current memory addr 100002 172526 100004 010040 MOV R0, -(R0) ; byte count, 2's compl, -2730 allows up to 2730 100010 012740 MOV #060003, -(R0) ; MTC command reg: 800bpi 9-trk, odd parity, 100012 060003 ; unit 0, no IRQ, extended bits zeroed, read+go 100014 000777 BR 0100014 This is the code for an RXV21 (RX02 floppy controller) which is one of the longer ones (the comments are mine): 1 000000 ; RXV21_boot From Microcomputer Interfaces Handbook 1983-84, page 484 2 000000 ; Use ODT to enter, then set RS=340, R6=1000, R7=1000, then P 3 000000 ; 4 000000 ORG O1000 5 001000 ; 6 001000 012700 MOV #O100240,R0 6 001002 100240 7 001004 012701 MOV #O177170,R1 ; RXCSR 7 001006 177170 8 001010 005002 CLR R2 9 001012 012705 MOV #O200,R5 9 001014 000200 10 001016 012704 MOV #O401,R4 ; track 1, sector 1 10 001020 000401 11 001022 012703 MOV #O177172,R3 ; RXDBR 11 001024 177172 12 001026 030011 BIT R0,(R1) 13 001030 001776 BEQ $-4 ; wait for TransferReq or Done 14 001032 100437 BMI O1132 ; branch if ERR set 15 001034 012711 MOV #O407,(R1) ; set DDens, Read, Go 15 001036 000407 16 001040 030011 BIT R0,(R1) ; wait for TR 17 001042 001776 BEQ $-4 18 001044 100432 BMI O1132 ; branch if ERR set 19 001046 110413 MOVB R4,(R3) ; give sector number 20 001050 000304 SWAB R4 ; swap track and sector 21 001052 030011 BIT R0,(R1) ; wait for TR 22 001054 001776 BEQ $-4 23 001056 110413 MOVB R4,(R3) ; give track number 24 001060 000304 SWAB R4 ; swap sector and track 25 001062 030011 BIT R0,(R1) ; wait for TR 26 001064 001776 BEQ $-4 27 001066 100421 BMI O1132 28 001070 012711 MOV #O403,(R1) ; EmptyBuffer (DDens) command 28 001072 000403 29 001074 030011 BIT R0,(R1) ; wait for TR 30 001076 001776 BEQ $-4 31 001100 010414 MOV R4,(R4) ; save sector number 32 001102 010513 MOV R5,(R3) ; set word count=256 33 001104 030011 BIT R0,(R1) 34 001106 001776 BEQ $-4 ; wait for done 35 001110 100410 BMI O1132 36 001112 010213 MOV R2,(R3) ; set address=0 37 001114 060502 ADD R5,R2 ; increment... 38 001116 060502 ADD R5,R2 ; ...address 39 001120 122424 CMPB (R4)+,(R4)+ ; bump R4 by 2 and clear all flags 40 001122 120427 CMPB R4,#3 ; sectors 1 and 3 get done 40 001124 000003 41 001126 003735 BLE O1022 ; loop if not finished 42 001130 012700 MOV #0,R0 42 001132 000000 43 001134 005007 CLR PC ; go to address zero 44 001136 120427 CMPB R4,#0 ; dummy operation, pipelined but not executed 44 001140 000000 There has to be *some* code *somewhere*, and different controllers need different boot code (if only because they have the registers at different addresses). There isn't any ROM on a KDF11-A or KDJ11-A, so you need there to be some bootstrap code on one of the other cards. Third-party controllers often have unique boot code on the card. Most DEC controllers rely on a boot ROM being on a special bootstrap board (like a BDV11, which also has a line time clock and bus terminators), a ROM board (like an MRV11-D) or a multifunction card (MXV11, which also has DRAM memory, clock, and serial lines for the console and one other serial device). Most of the DEC bootstraps for Qbus systems offer a choice of boot options (different disks, network, etc) and in addition will do a simple memory test (or at least write to it to ensure the parity or ECC is correct); many of the later ones are interactive. -- Pete Peter Turnbull Network Manager University of York