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From: keithd@cadovax.UUCP (Keith Doyle)
Newsgroups: net.micro.atari
Subject: Re: Atari 800XL superior to c64?
Message-ID: <365@cadovax.UUCP>
Date: Mon, 21-Jan-85 22:27:42 EST
Article-I.D.: cadovax.365
Posted: Mon Jan 21 22:27:42 1985
Date-Received: Thu, 24-Jan-85 19:35:45 EST
References: <212@eneevax.UUCP> <340@cadovax.UUCP>, <329@snow.UUCP>
Organization: Contel Cado, Torrance, CA
Lines: 135

[]
>I've been reading all these comparisons and I own a c64.
>I think that straight comparison is out, there are too many
>basic differances.

Who cares?  I'm learning a lot about the other guy.

>For a start the Atari machines have a display processor of sorts,
>that make the video very powerful, but the c64 has a versatile
>video controller that can tell the processor when to do things,
>via the raster interrupt, and thus if you wanted
>you could change video modes on every line also.
>This uses a lot of main processor time if used in many screen locations
>but can be used to give many effects not available using the display 
>file on an Atari,for example a one line pixel scrolling message anywhere
>on the screen.

This is performed in almost exactly the same manner on the Atari.  The
display list is a table of instructions for the display controller that
indicate what graphics (or text) mode is being displayed, and where the
data is coming from in memory.  Each mode takes up some number of raster
lines, and at the end of that mode, a new display instruction is fetched
to determine what the next mode is.  For example, the first display list
instruction can indicate a 2 color charater mode, starting from some
memory address.  This mode would take up 8 raster lines.  The next display
list instruction could specify a graphics mode that takes up a single
raster line. then another character mode, or several line graphics mode
line could be implemented.  Scrolling can take place merely by modifying
the display-list table's address pointer to the data for the specific line.
A display list instruction has a bit to signify an interrupt on a given
mode line.  The processor can then modify the color tables, move the pointer
to the character set data, move a players (sprites) horizontal location,
or some combinations thereof, and probably a few useful things I haven't 
thought of.  Interrupts are not required for scrolling, but the main
vertical interrupt is required as it sets up the initial pointer to the
display list table itself.  Multiple display list tables can be kept
in memory, so vertical interrupt routines can alternate or 'page-flip'
or whatever very simply.

>The disk interface speed in now effectively cured, with small
>alternative loaders. It now takes about 20sec to load 32k instead of
>1min30sec that it takes normally, since Atari use serial interfacing
>as well, I would assume that their disk speed is slower than this.

I wouldn't assume this, but I haven't timed it.

>As for memory, I can't compare the XL machines with the c64 since
>I'm not sure of the facts, but almost all commercial software is capable
>of access to the entire 64k of memory.

With the Atari, access to the entire 64k is available, but many applications
may not use it as it may eliminate a large part of their market which may
be in the 48k 800's out there.

>Sound, the Atari relies on fixed oscillators with which one can only
>make beeping noises (directly), the c64 has a synth which does more
>than most other people mentioned. For a start you have a choice of wave-
>form on all voices, this is for harmonic control. Triangle waves produce
>the least harmonics and sound more like most wind instruments,
>Sawtooth are very quite high up in harmonics, and pulse wave forms
>are like most other micro beeps except you can change the step/mark
>ratio. Finally there is the white noise generator, this is just another
>optional wave form, so can be used on all voices(unlike what others
>said). Next are the filters, there are digitally controlled
>high,low and band pass filters which can be used to make tinny
>sounds or bass sounds or whatever. Other features include
>ring modulation, hard sync., envelope shaping, A to D converter
>on voice 3, plus much more. I have heard very good speach synthesis
>on the c64 with no extra hard-ware(it really sounds like a person.)

In general, the C64 sounds like it has better sound generation characteristics,
however there is a very good software-only speech synthesizer that sounds
quite good that runs on the Atari.

>Graphics are next, the Atari highest mode is higher than that of
>the c64 I think, but what makes graphics in games is colour.
>The Atari is lousy at having a good range of colour on the screen
>at once, with careful planning on a c64 there is no reason
>why you can't use all 16 colours where you want when you want them,
>i.e. no trouble getting more than 2 colours on one raster line.

WRONG, you can get all 128 Atari colors on the screen at the same time.
There are modes that allow 16 colors, or 16 shades of 1 color, and with
display list interrupts, the entire color table can be modified at each
display mode line.  Color range is NOT a problem with the atari.

>The Atari sprites appear to be very limited too, why would one
>want a sprite filling the whole screen? Admittedly there are only
>8 sprites on the c64, but with the raster interrupts running
>then any number can be used, and they CAN move in both directions.

Rarely is a single 'sprite' used filling the whole screen.  Using display-list
interrupts, a single 'sprite' vertical stripe, can be divided up into many
individual ones.  (up to 192 ) with different horizontal positions.  Granted
vertical movement takes a byte move of the sprite data, but many times this
is not a lot of data, and can be done quickly.  With 4 vertical 'players'
(Atari's name for sprites) and 4 vertical 'missiles' (Atari's name for
2 bit wide sprites, can be combined to make a 5'th 8 bit wide player) this
adds up to a fair amount of graphics power.

>Software, this is where my favorite machine starts looking a
>little low, unfortunately where there are the same games on both
>the Atari and the c64 the c64 looks worse off, I can see no real
>reason why this is so, but I can only guess by saying that all of it
>was originally written on the Atari and then made to work on the c64.
>Thus when it designed all the graphics etc. were made to fit the Atari
>in particular and it was hard to move. Where software was made for
>the c64 (see Impossible Mission or Space Taxi) the quality is the
>best.

>In the case of support all I can say is that in England, where I live,
>Atari seems to have vanished, and there appears to be no support whatever
>despite all the Net News saying the 800XL is only about $120 over in
>America.

I must admit, even here in the U.S. (L.A. to be exact) support for Ataris
has kind of dried up.  You used to be able to see Atari's for sale in the
computer stores, with all the associated support.  However, this was back
when the 800's were selling for $600+.  Now the main source for Ataris is
toy stores and discount houses.  Up to date software supply is growing thin,
as the computer stores prefer the larger profit margin of IBM and Apple
wares.  This may be a phenomenon we all have to live with, and perhaps resort
to mail order if all else fails.  One hope, at least to Atari, would be the
success of their new 68000 product, which may re-inspire some stores to
carry the complete Atari line.  I hope so.  And/or perhaps the Amiga will
have a similar effect for C64 owners.


>		Dave (Maths @ Warwick University, UK)


Keith Doyle
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