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From: jml@tw-rnd.SanDiego.NCR.COM (Michael Lodman)
Newsgroups: comp.sys.ibm.pc,comp.sys.mac
Subject: Re: Multiple monitors (was: Xerox sues Apple!)
Message-ID: <200@tw-rnd.SanDiego.NCR.COM>
Date: 3 Jan 90 22:43:46 GMT
References: <2938@infmx.UUCP>
Reply-To: jml@tw-rnd.SanDiego.NCR.COM (Michael Lodman)
Distribution: usa
Organization: NCR Corporation - Distributed Systems Lab
Lines: 25

In article <2938@infmx.UUCP> aland@infmx.UUCP (alan denney) writes:
>Uh, Dave, how much have you used PCs?  As stated earlier, I have been running
>two monitors in my AT at home for quite a while, and I use them both for
>dual-screen debugging also.  What makes you think the PC world is incapable
>of such magic?
>close the machine, turn on the power.  No switches to set, no muss, no fuss.
>To switch primary monitor to the mono, run "mode mono".  To switch back to 

This is sort of an accident of addressing spaces in the PC. The mono cards
use a different base I/O address than do the color cards. I'm not sure if
this was an accident of design, or a wanted feature. However, it does
explain why only mono & (cga|ega|vga) will work. The BIOS will write to
only one of the I/O spaces depending on the video mode set. Some programs
bypassing the BIOS may use both monitors, but, it does not seem very
useful as very few programs take advantage of it.

The MAC's ability to use multiple monitors in a powerful way is one
of the few enviable features of that system.

-- 
+-----------------------------------------------------------+
| Michael Lodman               Mike.Lodman@SanDiego.NCR.COM |
| NCR Corporation  -  Distributed Systems Lab  -  San Diego |
| 9900 Old Grove Rd.  San Diego, CA.  92131  (619) 693-5353 |
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