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Path: utzoo!mnetor!seismo!columbia!rutgers!cbmvax!grr
From: grr@cbmvax.cbm.UUCP (George Robbins)
Newsgroups: comp.sys.amiga,comp.graphics
Subject: Re: PC2 Graphics beats Amiga
Message-ID: <1822@cbmvax.cbmvax.cbm.UUCP>
Date: Sat, 2-May-87 17:10:05 EDT
Article-I.D.: cbmvax.1822
Posted: Sat May  2 17:10:05 1987
Date-Received: Tue, 5-May-87 04:42:45 EDT
References: <500@titan.camcon.co.uk> <3062@sdcsvax.UCSD.EDU> <1794@cbmvax.cbmvax.cbm.UUCP> <3073@sdcsvax.UCSD.EDU>
Reply-To: grr@cbmvax.UUCP (George Robbins)
Organization: Commodore Technology, West Chester, PA
Lines: 37
Keywords: Kill this subject quick
Xref: mnetor comp.sys.amiga:4469 comp.graphics:604

In article <3073@sdcsvax.UCSD.EDU> hutch@sdcsvax.UCSD.EDU (Jim Hutchison) writes:
>In article <1794@cbmvax.cbm.UUCP> grr@cbmvax.UUCP (George Robbins) writes (<)
>
><	Uh, they use shift-register "video" rams which means bandwidth is
><	not a real issue.  This is pretty easy on the simplistic display
><	model that IBM implements.
>
>You can still do processing on the contents of the shift-register.  Not
>permanent block transfers, more like inserted block transfers.  Just insert
>the little devil into the output stream.  Is this a silly way to handle such
>things?  Sounds like a fine way to do live video overlay, but I could be
>quite confused.

Oops, I should have less cryptic.  What I meant by "simplistic" is that the
IBM displays have a small chunk of display memory, which is mapped in a
pretty much one-for-one way to the display.  This is easy to do with video
rams.

The Amiga, on the other hand, can display a fairly random assortment of
bitplanes and sprites from arbitrary regions in display memory.  This is not
so easy to do with video rams.

For the uninitated, video or "shift-register" DRAMs have both the normal
processor interface and an extra high-speed serial data path.  The two
accesses only conflict when a new page of data needs to be transfered to
the serial output section.  This is obviously a considerable improvment
over having the display and the processor try to share the same data path.

The tradeoff with respect to the Amiga is that, unless you want to make
things a lot more complicated than otherwise neccessary, bitplanes would
need to be aligned to conform with the underlying hardware.  Also, horizontal
scrolling becomes less pleasant.

-- 
George Robbins - now working for,	uucp: {ihnp4|seismo|rutgers}!cbmvax!grr
but no way officially representing	arpa: cbmvax!grr@seismo.css.GOV
Commodore, Engineering Department	fone: 215-431-9255 (only by moonlite)