Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!pacbell!att!cuuxb!mmengel
From: mmengel@cuuxb.ATT.COM (Marc W. Mengel)
Newsgroups: comp.windows.x
Subject: Re: Contents of windows (Really Amiga)
Keywords: LoTech
Message-ID: <2771@cuuxb.ATT.COM>
Date: 4 May 89 18:21:02 GMT
References: <4434@stiatl.UUCP> <4037@ficc.uu.net> <8078@phoenix.Princeton.EDU>
Reply-To: mmengel@cuuxb.UUCP (Marc W. Mengel)
Organization: AT&T-DSD, System Engineering for Resellers, Lisle IL
Lines: 40

In article <8078@phoenix.Princeton.EDU> mbkennel@phoenix.Princeton.EDU (Matthew B. Kennel) writes:
>>of the hardware, 640K sounds like scads of memory. The Amiga runs in 512K
>>with both the application and the windows sharing that memory.

>Can the Amiga run the whole server and clients in 512K of memory, when
>that 512 also includes the frame buffer???  It MUST have shared libraries
>then, which many Eunixes seem to lack.
>
>I think the Amiga's choice to make backing store available for every window
>and then return errors when it's out of memory seems like a mistake: I would
>rather have things work but run slowly than crash quickly.  By extension, 
>why have virtual memory at all?  Just return an error code when it runs out.

The Amiga does it this way because that is how its native windowing system
works; which in turn is based on its hardware architecture.  (If I recall
correctly) the Amiga low level graphics routines take a pixmap-ish
structure that the *application* program owns and has allocated, and 
hardware bitblits it onto the frame buffer for the screen.  These
same low-level libraries also maintain things like animation objects
cruising accross the screen, etc. and may in fact just make the video
chip look at your bitmap instead of the screen bitmap temporarily
to display it, rather than copying it onto the screen at all.  By making
the X server use this paradigm as well (which forces it to keep backing
store for everything) X server windows can live on the same screen as normal
Amiga windows.  Using the already written Amiga graphics library (which
does basically everything an X server needs to do) gets you all kinds
of performance wins, because the graphics coprocessor does most of the
work for you.

The Amiga 500 currently does not have virtual memory... of course it also
costs only ~$500.

>>Peter da Silva, Xenix Support, Ferranti International Controls Corporation.
>Matt Kennel	mbkennel@phoenix.princeton.edu


-- 
 Marc Mengel					mmengel@cuuxb.att.com
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