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From: allen@basalt.uucp (Allen Akin)
Newsgroups: comp.graphics,comp.sys.dec
Subject: Re: DECstation 5K PXG/Turbo graphics
Message-ID: <1990Aug29.221712.17018@wrl.dec.com>
Date: 29 Aug 90 22:17:12 GMT
References: <10338@pt.cs.cmu.edu>
Sender: news@wrl.dec.com (News)
Reply-To: allen@atd.dec.com (Allen Akin)
Organization: DEC Advanced Technology Development, Palo Alto, CA
Lines: 38

In article <10338@pt.cs.cmu.edu> cbs@cad.cs.cmu.edu (Clauss Strauch) writes:
>
>	[...]
>	-- What are the advantages(besides speed) of getting a PXG with
>	the optional Z buffer, vs. a PXG Turbo?

Functionally, a 24-plane PXG is identical to a PXG Turbo.  Only the
performance differs.

In a nutshell, the PXG has:

	40MHz i860 for geometry acceleration
	One 5x1 array of pixel engines running at 80ns
	Two image buffers (8 or 24 planes each)
		240ns random access time, 80ns page-mode access time
	Optional Z-buffer (always 24 planes)
		240ns random access time, 80ns page-mode access time

The PXG Turbo has:

	44MHz i860 for geometry acceleration
	Two 5x1 arrays of pixel engines running at 60ns
	Three image buffers of 24 planes each
		180ns random access time, 60ns page-mode access time
	Z-buffer with 24 planes
		180ns random access time, 60ns page-mode access time

The Turbo offers about 10% improvement over the standard PXG in
geometry acceleration, about 160% improvement for large-area pixel
fills and aligned pixel copies, about 100% improvement for polygon
rasterization, and about 35% improvement for vector rasterization.  The
extra 24 planes of image buffer are useful for storing images for fast
access -- for panning, antialiased image accumulation, background data
for cartography, additional drawing layer for MCAD, etc.

Followups to comp.sys.dec.

Allen