BI Bus

From: Roger Ivie <IVIE_at_cc.usu.edu>
Date: Mon Jun 28 15:13:05 1999

Ack! How could I miss a discussion of the BI bus? I'd better pay a bit
more attention when I'm glancing through the subject lines...

> It was open for a minimal definition of the word open.
> DEC owned the chip set and protocol and would sell you the chip set
> if your board was not a competitor to a DEC board.

I can vouch for this. The company I used to work for did a couple of
VAXBI interface boards: a quad IEEE-488 board and an interface to a
custom shared memory. DEC had to be convinced where product was
complementary before it gave you the right to buy chips.

> A number of outfits purchased the older lowest priced DEC board
> available to pull the chips for the BI bus to make disk controllers
> and such since DEC wasn't going to let anyone reverse engineer the set
> without a major patent fight.

There was a memory company that reverse engineered the BI bus, at least
enough to build memory cards. Clearpoint, perhaps? I don't recall which.
IIRC, they were bought by an I/O company (Emulex, maybe?) primarily to
gain access to their reverse-engineered BI chip.

> DEC cut it's own throat on this one and the BI bus never took hold.

There's also the fact that for the average bus transaction it really
wasn't any faster than the UNIBUS. You had to _always_ do
octaword transactions to outperform the UNIBUS (at least, the theoretical
max of the UNIBUS; and by the time the VAXBI appeared, it was starting to
be possible to get the theoretical max out of the UNIBUS. I once did a
processor module that did the UNIBUS mapping during the settle(?) (the one that
was after the deskew time) time; once that 75ns was up, the processor module
knew that the adders had had enough time to map the address and didn't need to
add any extra delay for the mapping. The processor module could
support a J-11 running full bore while simultaneously outperforming the
PDP-11/84 on DMA throughput. And it looked enough like a PDP-11/84 to
run RSX-11 out of the box).

> who left DEC around the time of the BI bus release... and has NO
> proprietary data on 'em.

I've still got a couple of copies of the VAXBI manual.

Roger Ivie
ivie_at_cc.usu.edu
Received on Mon Jun 28 1999 - 15:13:05 BST