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From: jdb@mordor.ARPA (John Bruner)
Newsgroups: net.micro
Subject: Re: 192000 on a Mac, (was update on **real** 19200 CRT)
Message-ID: <14734@mordor.ARPA>
Date: Wed, 20-Aug-86 11:33:53 EDT
Article-I.D.: mordor.14734
Posted: Wed Aug 20 11:33:53 1986
Date-Received: Thu, 21-Aug-86 01:27:51 EDT
References: <671@mordred.purdue.UUCP> <71@winfree.UUCP>
Reply-To: jdb@mordor.UUCP (John Bruner)
Organization: S-1 Project, LLNL
Lines: 16
Keywords: Amiga,Macintosh, calculator gymnastics, scrolling speed

>>In fact, one of the design goals of the mac was that
>>it be fast enough to simultaneously write to the floppy, read characters
>>at 19200, and display them on the screen!
>Of course this was done by slowing the floppy down to the point that
>no one would want to write the floppy while doing anything else.

Actually, noone *can* write to the floppy while doing anything else,
unless they write their own specialized code which manipulates the
hardware directly.  The IWM requires busy-wait CPU attention; it is
not interrupt-driven and it cannot tolerate other interrupts.  In order
to avoid losing input on (only) one serial port the disc driver code has
to poll the SCC (serial interface) while it's spinning on the disc.
-- 
  John Bruner (S-1 Project, Lawrence Livermore National Laboratory)
  MILNET: jdb@mordor [jdb@s1-c.ARPA]	(415) 422-0758
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