8 Nov
2017
8 Nov
'17
9:18 p.m.
On Wed, Nov 8, 2017 at 8:02 PM, Noel Chiappa <jnc(a)mercury.lcs.mit.edu>
wrote:
If one were using a serial line
hooked up to a DZ (and those were common - DH's were _much_ more
expensive, so
poor places like my lab at MIT used DZ's), then _every character printed_
caused an interrupt.
Right, although many (most) Unix sites used Able DHDM's which were cheaper
than DEC DZ's, took less space in the backplane, had full modem control
(inc RTS/CTS handshaking in HW) and were DMA. But, my memory is that they
did not show up until '78 though.
The truth is DZ sucked from a performance standpoint. Besides not being
able to support RTS/CTS flow control, the 8 serial ports shared an input
buffer in the HW IIRC and the UART only had 2 chars of buffering. An
8-port DZ with all lines running 19.2K baud could kill a 780. People
that ran the "Berk-net" (which a pre-TCP networking system for UNIX that
ran on serial lines) needed spread out the Berk-Net load between different
DZ lines. No so if you have Able gear.
So I'll take the 'common' note to be if you used a 'pure DEC' set
up - you
used DZ-11s. But as you said most of us were looking at costs, so
'foreign' peripherals were also 'common' in the UNIX community.
DH11's
were preferred.