18 Feb
2022
18 Feb
'22
1:41 p.m.
On Feb 18, 2022, at 4:30 PM, Chris Zach via cctalk
<cctalk at classiccmp.org> wrote:
XMI already existed as the system bus for the VAX
6000 series machines. I/O on the VAX 6000's was via an XMI-to-BI bridge. I
don't remember the exact performance specs on XMI, but it was wider and faster than
BI.
I thought XMI was only supposed to be a CPU/memory bus, with IO being done by multiple
VaxBI busses. That's what we had on the 6000 at the computer Society: 2 CPUs, memory,
and two VaxBi with a SCSI disk controller on each. From what was just reported, the 6000 series indeed did
it that way. But I think on the 9000 it was an I/O bus too. I definitely remember some
work on XMI based I/O devices, in particular an FDDI card. And indeed you can find a spec
for that device in http://www.bitsavers.org/pdf/dec/xmi/ .
paul