From: simon@ivem.ucsd.edu (Simon Lee)
Newsgroups: rec.games.video
Subject: Re: SEGA CD Commercial
Date: 6 Nov 1992 01:46:06 GMT
Organization: University of California, San Diego
NNTP-Posting-Host: ivem.ucsd.edu

In article <1992Nov5.210211.6109@unocal.com> stgpkdh@st.unocal.com (Kevin Hammel) writes:
>In article <1992Nov5.173746.9237@megatek.com>, max@megatek.com (Max Elliot) writes:
>
>|>     Frame Buffer:
>|> 
>|>        the video RAM from which the actual picture is drawn.
>|>        It may have an arbitrary bit depth, and this determines
>|>        the number of colors (or greyscales) that may be displayed
>|>        AT ANY ONE TIME on the screen.
>|> 
>|>     CLUT or Color Lookup Table:
>|> 
>|>        A register of RGB values for the guns in the monitor which are
>|>        accessed via values in the frame buffer. The number of bits in
>|>        THIS table determines the TOTAL available colors, not the number
>|>        displayable at any one time.
>|> 
>|>   Some architectures use a CLUT, some do not. (in which case the bit-depth
>|>   of the frame buffer determines the TOTAL available colors and the number
>|>   displayable at one time) There are also variations on both of these
>|>   schemes. When discussing number of available colors etc. make mention
>|>   of the architecture so that it is clear what is really being said.

I understand all this.  I thought I said the above.  Oh well, better proofread
before posting :)

>The problem is that data transfer off of the CD ROM is somewhat less than 200 K
>bytes/second (I don't think  SEGA is using a double speed drive),
>so the Genesis with its 3xx by 2xx screen (Not sure of exact resolution) will only
>be able to fill the frame buffer around 3 times per second IF it is reading directly off
>of the CD ROM, with NO compression, AND all  64 displayable colors are used.  This is
>why tne number of colors/ size of screen is reduced for increased framerate, as fewer
>colors or smaller screen means less data per frame, and more frames can be read in per
>second.  SEGA has claimed that the machine will show 16 colors 3/4 screen at 15 fps.
>That is all I wanted to say.
>

Ok.  Now I understand what you're trying to say.  The thing about the Sega CD,
though, is it has internal ram (I don't remember how big, 8 Megabits?)  that
will allow the data from the CD to be read into first.  This will allow for
30fps(?) at full color resolution.  The SegaCD doesn't play off the CD, but it
reads the data off from the CD into it's internal ram.  That's how it can have
the full color resolution, without data rates coming into play.  That's why
I said it only affects how much delays are introduced between levels or
whatever takes place.  If it needs to load in more graphics data, you'll get a
slight delay, but after the data is loaded, you won't see any degradation in
visual quality or speed.  In fact, with the faster 68000, the play should be
a lot smoother, hopefully :)

-

-- 
*   Simon Lee              *   Microscopy and Imaging Resource          *
*   simon@ivem.ucsd.edu    *   Intermediate Voltage Electron Microscopy *
*   sulee@ucsd.edu         *   UC San Diego, Dept. of Neuroscience      *
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