Thursday, December 12, 2013

What I learned from my Atari 8-bit days

Happy Throwback Thursday! Some time ago, also on Throwback Thursday, I tweeted a link to a document I wish I had when I was much younger:

I wish I'd had it, because it may have helped me save my first 8-bit Atari computer (an 800XL) from having its POKEY chip fried by a dumb copy-ROM-into-RAM loop. Beyond learning not to blindly write into hardware registers, my Atari 8-bits ended up teaching me a surprising amount. A fair amount of what I learned helped me mature into a proper Computer Scientist and Software Engineer.

Be Careful of the Next Version

I generally look forward to upgrades. Bugs get fixed, features get added, things move faster, and if you're really lucky, you get more than one of those with one upgrade. It doesn't always turn out nicely, though. Sometimes, the next version changes things enough where things that once worked no longer do. Other times, the next version just plain sucks.

8-bit Atari owners had two serious negative encounters - one of each kind. The unexpected change was the transition from the original 400 & 800 models to the XL (and later XE) series. The reason this was a problem is actually best described later.

Atari's DOS (almost every 8-bit machine's disk drivers were called "DOS") lingered on version 2.0 from 1980 until 1984. To accompany new "enhanced density" 5.25" floppy drives, Atari released DOS 3. DOS 3 falls squarely into the, "just plain sucks," category. It was a poor design, including such misfeatures as:

  • Larger block sizes (2048 bytes vs. 128 bytes), which lead to wasted disk space and sometimes less overall capacity if anything barely spilled into the next block
  • One-way migration. Once your data moved to DOS 3, it wasn't going back.
  • An overbearing help system that took up disk space (already at a premium).
I didn't know what it was called at the time, but DOS 3 suffered from the Second-System Effect. Luckily, Atari ended up offering DOS 2.5, which looked like DOS 2.0, save for both support for enhance-density floppies, AND the ability to migrate DOS 3 files back to DOS 2.x.

Declare Your String Sizes

Jumping from Pascal or even BASIC to a language like C could be confusing to some. "What do you mean strings are just a character array?" If you cut your teeth on Atari BASIC, you already had an inkling of what was going on.

The classic Microsoft BASIC took up more than the 8K bytes that 8-bit Ataris had reserved for the cartridge slot. The resulting shrinkage of Atari BASIC included the array-like requirements for strings. On classic Microsoft BASIC:

But you had to declare the string size in Atari BASIC:

5 DIM A$(100)
One could not have an array of strings in Atari BASIC, and some of the classic BASIC array operators took on new significance in Atari BASIC. See here for a treatise on the subject.

Don't Depend on Implementation Details

I mentioned the transition from the 400 and 800 to the XL series. Several pieces of software broke when they loaded onto an XL. The biggest reason for this was because these programs, to save cycles, would jump directly into various ROM routines that were supposed to be accessed through a documented table of JMP instructions. To save the three cycles of an additional JMP, programs would often inline the table entries into their programs. The XL series included a rewritten ROM, which scrambled a large portion of where these routines were implemented. BOOM, no more working code.

Atari, to their credit, released a "Translator" boot disk, which loaded a variant of the old 800 ROM into the XL's extended, bank-switched, RAM, and ran the system using the old 800 ROM. This allowed the broken software to continue to work.

You WILL Have Rejected Submissions

Owning an 8-bit Atari meant you subscribed to at least one of Antic or ANALOG. I was an ANTIC subscriber until I graduated high school. I even tried to submit, twice, type-in programs with accompanying articles to ANTIC. Both were terrible, and rightly rejected by the editor. I'm honestly afraid to remember what they were.

And William Gibson's a Pretty Good Writer

Speaking of Antic , check out this article from September, 1985, especially Part 3 of the article. I immediately scoured the Waukesha County Library System trying to find Neuromancer, and wasn't disappointed... not at all. 16-year-old me really liked this book, and wouldn't have discovered it before college were it not for ANTIC, which I'd have not read without my 8-bit Atari.

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