Well, an executable format screen is one where the CPU is needed to display the picture. Ataris can do that stuff, often to great effect! A mode change here, color register stuff there, sprite positioned here, overlap priority / see through there...
There are "stock" graphics that just kind of happen with a minimum of CPU intervention after setup. On Ataris, there is always some setup with the display list, etc...
There are "not-stock" graphics that are possible, and that require the CPU to do stuff to make the display continue to happen beyond the setup actions always required. That's executable format in simple terms.
Some stuff I think is awesome:
1. I really liked Atari Basic. It was a non-Microsoft variant, and it could do some great tricks! One of those was boolean operators in expressions:
50 x = x + ((Y < 50)*5)
Y is compared to 50, and if less, the expression evaluates to "1", which is "true", which is then multiplied by 5, finally the product of that was added to x.
30 IF (y < 50) THEN X = X + 5
That's basically the same thing, done in ordinary BASIC terms.
Atari BASIC utilized a variable location table, meaning strings could be mapped to the display memory. One could do scrolling with a simple A$(40) = B$ kind of thing, where the index into one string was one row off, producing the scroll. This could be used to move PM graphics too, as they had no vertical positioning capability otherwise. I made big use of the string trick early on, the best example would have been a BREAKOUT game with scrolling bricks...
2. The SIO system, is basically device independent I/O. The authors of the Atari ROM did very well, packing in a lot of nice functionality into a small space. Some advanced concepts in there still seeing extension and use today.
3. Some of the case designs. I have kept an Atari 400 around just for that reason. I know the keyboard is basically impractical, but the machine just looks so damn cool otherwise! I really liked the XL series too, the 800 XL my personal favorite.
4. Games! Each machine has these, and they all have a texture that comes from the hardware. Ataris are no different. Since I grew up with a VCS, the Atari computers follow with the same kind of awesomeness. YMMV, of course, depending on what you had and where you live.
5. Colors. How the Atari computers generated color really appeals to me. It's got it's limits, compared to other machines with a better color signal, but I gotta say I just like 'em. At the time, features like color redirection were pretty high end things.
6. The hardware story. Atari computers have a very interesting hardware combination. Over the years a lot has been done, discovered, hacked, etc... They are fun machines to follow. Many 8 bitters are. The POKEY, ANTIC, GTIA, PIA is a fun hardware playground with a lot of interesting features, and it's very flexible. Atari computers could more or less damn near fill an entire video frame. One of the few 8-bitters that can do wide-screen display, for example. Tons of info here, and I think it's all just awesome compared to simpler machines. There are trade-offs for that though. Always is.
7. Controllers. To me, this is one of the most awesome things, because the Atari computers got all the fun VCS controllers. So a person could get real paddles, analog joysticks (if desired and programmed for as the home computer line never saw an analog control, but the game console 5200 did, but still...), trac-balls, mouse, keyboard, joystick, rotary driving controller, etc...
Today, I think these are fun to program for. Lots of varied input options.
8. I/O, particularly on the 400/800. The controller ports were bi-directional. As a kid, I utilized this to do basic electronics stuff, controlling things with the old 400, using the higher numbered ports to interface with other things. The controller buttons are latched too, allowing for detection of input even when the CPU misses it's polling window. Simple stuff, but well engineered and very useful.
9. For me, MAC/65 cartridge assembler. While it was an add-on, it was a good one. Powerful, fast, etc...
Edited by potatohead, Mon Apr 23, 2012 2:00 PM.