From mboxrd@z Thu Jan  1 00:00:00 1970
From: jnc@mercury.lcs.mit.edu (Noel Chiappa)
Date: Mon, 28 May 2018 22:55:11 -0400 (EDT)
Subject: [TUHS] Control-T (was top)
Message-ID: <20180529025511.C6E0318C08A@mercury.lcs.mit.edu>

    > From: Paul Winalski

    > DZ11s ... the controller had no buffer

Huh? The DZ11 did have an input buffer. (See the 'terminals and communications
handbook', 1978-79 edition, page 2-238: "As each character is received ...
the data bits are placed ... in a .. 64-word deep first-in/first-out hardware
buffer, called a 'silo'.")

Or did you mean output:

    > if you were doing timesharing it could bring the CPU to its knees in
    > short order

The thing that killed an OS was the fact that output was programmed I/O, a
character at a time; using interrupt-driven operation, it took an interrupt
per character. So for a 9600 baud line, 9 bits/character (1 start + 7 data + 1
stop - depending on the line configuration), that's about 1000 characters per
second -> 1000 interrupts per second.

The DH11 used DMA for output, and was much easier on the machine.

	Noel