Path: utzoo!attcan!uunet!lupine!ed
From: ed@lupine.UUCP (Ed Basart)
Newsgroups: comp.windows.x
Subject: Re: ASCII terminals vs. X Window System terminals
Summary: 10 stations on a Sun IV
Message-ID: <153@lupine.UUCP>
Date: 20 Jan 89 16:26:08 GMT
References: <8901172105.AA06900@hydra>
Organization: Network Computing Devices, Palo Alto, CA
Lines: 29

There are two ways that I use to think about how an X display station (aka X
terminal) affect host systems.  The first way is to imagine that the X
station replaces a "dataless" Sun 3/50.  The traffic that one finds between
the workstation and the various hosts is essentially the same (especially
if the Sun user is an X user) as with an X station.  Note that dataless
Suns have a small local disc to take care of booting and paging, so this
activity is not on the net.  This means that if you know the dataless
workstation/server ratio, you can use the same ratio for X stations.

The second model is to make the display station do terminal activity, just
like a terminal.  This means receiving input from the keyboard (I'll
ignore the mouse in this comparison), and blasting the screen with characters.
All comparisons that I've ever seen has shown output to outweigh input by
a large factor, so I'll just talk about output.

In our shop we have connected 10 stations to a Sun IV, and had them all
"cat"-ing away.  If memory serves me well, we measured an aggregrate
throughput of 45,000 characters/second before the Sun ran out of gas (100%
cpu utilization).  I've never tried the same test using real terminals
(especially ones that can run at 4,500 characters/second), but my guess is
no more than 20 terminals can be run at full speed by a Sun.  

Now I know that real terminal users are interactive and what's really
important is to measure a "transaction", which is typing a key and getting
it echoed.  The important measure is response time, and the maximum number
of people typing before response time begins to vary.  Once we can establish
such a benchmark, we'll have a better measure.  However, as has been
pointed out, it's not clear how relevant it is to limit the X station to
behave just like a terminal.