[HECnet] VS4000/90: Up and running!

[Johnny Billquist]

On 2013-02-08 23:31, Jordi Guillaumes i Pons wrote:

El 08/02/2013, a les 23:14, Johnny Billquist <bqt at softjar.se> va escriure:

And the problem is just that the boot rom uses a more restricted disk block addressing, limiting the
booting to disks of less than 1G. (Actually, you can boot from larger disks as well, as long as the boot
rom don't need to read from anything above 1G.)

Nice to know. IIRC I read about the firmware dropping the high bits of the block address so at some point
in time the writes against the disk would "wrap around" and trash the first 4GBs... but it seems its quite
an urban legend :)

No. That is correct. And it's 1G, not 4G. SCSI commands comes in some different flavors. Old VAXstations (and some others) used 6 byte SCSI commands, which limited the block numbers to 20 bits (some say 21, but I think it is 20). Later systems use 10 byte SCSI commands, which allows for 32 bit block numbers.

What happens is that if you go above 20 bits in the SCSI commands of those old VAXen, they will just use the low 20 bits of the block number, so you will indeed wrap.

See http://labs.hoffmanlabs.com/node/218 if you want a few more details.

BTW, This is a nice sight:

$ sh net
VAX/VMS Network status for local node   7.61 BITXOO on   8-FEB-2013 23:26:08.76

The next hop to the nearest area router is node   7.60 BITXOV.


                Node                   Links   Cost   Hops     Next Hop to Node

          7.61     BITXOO             0         0         0         (Local)     ->   7.61     BITXOO
          7.6       MBSERV             0         3         1         UNA-0         ->   7.6       MBSERV
          7.60     BITXOV             0         3         1         UNA-0         ->   7.60     BITXOV
          7.64     BITXO1             0         3         1         UNA-0         ->   7.64     BITXO1
          7.65     BITXO2             0         3         1         UNA-0         ->   7.65     BITXO2
          7.67     BITXO4             0         3         1         UNA-0         ->   7.67     BITXO4
          7.68     BITXO5             0         3         1         UNA-0         ->   7.68     BITXO5
          7.70     BITXOT             0         3         1         UNA-0         ->   7.70     BITXOT
          7.71     BITXOR             0         3         1         UNA-0         ->   7.71     BITXOR
          7.72     BITXOM             0         3         1         UNA-0         ->   7.72     BITXOM
          7.74     BITXOW             0         3         1         UNA-0         ->   7.74     BITXOW
          7.79     BITXT0             0         3         1         UNA-0         ->   7.79     BITXT0

:-)
Emulated Unibus-machine, or the real deal?

	Johnny

-- 
Johnny Billquist                                   || "I'm on a bus
                                                                  ||   on a psychedelic trip
email: bqt at softjar.se                         ||   Reading murder books
pdp is alive!                                         ||   tryin' to stay hip" - B. Idol