[TUHS] pre-more pager?

Ron Natalie ron at ronnatalie.com
Thu Nov 9 06:28:18 AEST 2017


We actually still had some real DEC DH’s on our system.   These are what the DHDM emulates, but are implemented in its own backplane full of various flipchip cards.

 

At least the DZ doesn’t loop on the ready bit like the kernel printf (not to be used for idle chit-chat)..

 

From: TUHS [mailto:tuhs-bounces at minnie.tuhs.org] On Behalf Of Clem Cole
Sent: Wednesday, November 8, 2017 3:19 PM
To: Noel Chiappa
Cc: TUHS main list
Subject: Re: [TUHS] pre-more pager?

 

 

 

On Wed, Nov 8, 2017 at 8:02 PM, Noel Chiappa <jnc at 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.

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