History of Atari 8-bit Computers

Built-in and disk operating systems The startup screen of early Atari 8-bit models when no program is loaded. The startup screen when ATARI BASIC is selected.The Atari 8-bit computers came with an operating system built into the ROM. The Atari 400/800 had the following:

OS Rev. A – 10K ROM (3 chips) early machines.
OS Rev. B – 10K ROM (3 chips) bug fixes. Most common for 400/800.
The XL/XE Atari 8-bit models all had OS revisions due to added hardware features and changes. But this created compatibility issues with some of the older software. Atari responded with the Translator Disk, a floppy disk which loaded the older 400/800 Rev. B or Rev. A OS into the XL/XE computers.
OS Rev. 10 – 16K ROM (2 chips) for 1200XL Rev A
OS Rev. 11 – 16K ROM (2 chips) for 1200XL Rev B (bug fixes)
OS Rev. 1 – 16K ROM for 600XL
OS Rev. 2 – 16K ROM for 800XL
OS Rev. 3 – 16K ROM for 800XE/130XE
OS Rev. 4 – 32K ROM (16K OS + 8K BASIC + 8K Missile Command) for XEGS

The XL/XE models also came with built-in Atari BASIC. Early models came with the notoriously buggy revision B. Later models used revision C.

The standard Atari OS only contained very low-level routines for accessing floppy disk drives. An extra layer, a disk operating system, was added to assist in organizing file system-level disk access. Enter Atari DOS, which, like most home computer DOSes of the era, had to be booted from floppy disk at every power-on or reset. Unlike most others, Atari DOS was entirely menu driven.

DOS 1.0 – Initial DOS for Atari.
DOS 2.0S, 2.0D – Improved over DOS 1.0, became the standard for the 810 disk drive. 2.0D was for never-released 815 drive.
DOS 3.0 – Came with 1050 drive. Used a different disk format from previous DOSes, and was incompatible with DOS 2.0, making it very unpopular. The only command-line Atari DOS.
DOS 2.5 – Replaced DOS 3.0 in later 1050s. Functionally identical to DOS 2.0S, but able to read and write Enhanced Density disks.
DOS 4.0 – Designed for 1450XLD, cancelled, rights given back to the author.
DOS XE – Designed for the XF551 drive.
Several third-party replacement DOSes were also available. See Atari DOS under Third-party DOS Programs.

Available programming languages

Action! – A product of Optimized Systems Software. A high performance language that compiled to machine code, with good support for Atari’s hardware. While it was popular with hobbyists, it never attained widespread acceptance, particularly since it was limited to the Atari 8-bit platform.

Assembly language

Atari Assembler Editor – A 6502 assembler editor and compiler was released by Atari in a ROM cartridge.
Atari Macro Assembler (AMAC) – A macro assembler released by Atari Program Exchange (APX) in disk form. Copy protected.
MAC/65 – 6502 macro assembler/editor developed by Optimized Systems Software. Released in disk and cartridge forms.
Synassembler – Assembler from Synapse Software. Written by Steve Hales. Not compatible with XL/XE computers without patching.
Macro Assembler/Text Editor (MAE) – Assembler from Eastern House Software. Written by John Harris. BASIC dialects.
Atari BASIC – This was the original BASIC for the Atari 8-bit family. Came as a ROM cartridge with the Atari 400/800 models, but was built into the computer’s ROM in later models. In the XL/XE models, BASIC could be disabled by holding down the OPTION key while booting.
Atari Microsoft BASIC – A version of BASIC for the Atari 8-bit family released by Atari that was more compatible with Microsoft BASIC. Microsoft BASIC II was the same except it was in a ROM cartridge plus extension disk.
Turbo Basic XL – An improved version of Atari BASIC released by a third party that is not only faster, but offers many more commands. There is also a compiler that makes Turbo-BASIC XL programs even faster by compiling them into machine-language binaries.
BASIC A Plus — An extended BASIC from Optimized Systems Software
BASIC XL — An improved BASIC from Optimized Systems Software
BASIC XE — An enhanced version of BASIC XL from Optimized Systems Software

Deep Blue C – A C compiler. Written by John Palevich, APX.
LISP
INTER-LISP/65
LOGO
Atari LOGO
PILOT
Pascal
Atari Pascal – Required two drives.
Draper Pascal
Kyan Pascal

Forth
After Atari’s 8-bit machines entered the realm of retrocomputing in the late 1990s, cross platform development tools such as XASM, TASM, and cc65, most commonly run on PCs, have been much used by enthusiasts to do programming intended for the machines.

Graphics capabilities
While the ANTIC and GTIA chips allowed a variety of graphics modes to be combined, and different playfield widths to be used, the Atari’s Operating System provided a basic set of graphics modes. In most cases, these were exposed to Atari BASIC via the “GRAPHICS” command, and to some other languages, via similar system calls. 40×24 text modes 1 color of text, with each character’s 8×8 pixels the same size as those in 320×192 graphics mode, with the same hue restriction. Characters with the high-bit on were represented in inverse-video.

“Lowercase with descenders” mode, which was not available through GRAPHICS, only as part of custom display lists. In this mode characters were 10 pixels high and occupied either the upper or lower 8 pixels of that height. This was not strictly speaking a 40×24 text mode, because of the unusual height. Colored text, where every two bits represents a colored pixel (characters were 4×8 pixels that were the same size as those in 160×192 graphics mode). Characters with the high-bit on were displayed using a 5th color palette registered where the 4th would normally be used. Colored text, where every four bits represents a colored pixel (characters were 2×8 pixels that were the same size as those in 80×192 graphics mode and had the same color limitations). This mode was not directly available through GRAPHICS but required setting GTIA flags in text mode.

20×24 text mode
1 color of text, with each character’s 8×8 pixels the same size as those in 160×192 graphics mode. Characters with various bits enabled or disabled (which would normally appear as ‘control-characters’, lower-case characters, or inverse-video) were displayed with different colored pixels.
20×12 text mode (Same as 20×24 text mode, but with larger pixels and fewer rows of text)
40×24 graphics mode — 4 colors (2bpp)
80×48 graphics modes — Either 2 colors (1bpp), or 4 colors (2bpp)
160×96 graphics modes — Either 2 colors, or 4 colors
160×192 graphics modes — Either 2 colors, or 4 colors
320×192 graphics mode — 2 colors (1bpp). The pixels were a shade of the playfield color, and could not be different hue.
80×192 graphics modes (GTIA chip only)
9 colors from the color palette registers
All 15 Atari hues, but only of one brightness (plus black)
All 16 Atari shades, but only of one hue

Software-driven modes
In 1992, Jeff D. Potter created a GIF decoder and image viewer for the Atari called APACView. APAC, or Any Point, Any Color, was a software-driven method of display an image using all 256 of the Atari’s possible colors. By taking 80×192 mode lines that displayed 16 hues, and those that displayed 16 shades, and either interlacing rows of them, quickly alternating between rows of them, or both, a screen displaying 80×96 or 80×192 pixels in 256 colors could be perceived.

Later, Potter created another GIF decoder, and later a JPEG decoder was created, which broke an image into the three red, green and blue channels. 16 shades of each, at 80×192 pixels, would be displayed in an interlaced and flickering fashion. The human eye’s persistence of vision would allow the viewer to see 4096 colors (12bpp) at 80×192, with slight ‘rolling’ artifacts in solid red, green or blue fields in the image. This was called ColrView mode.

In 1994, Clay Halliwell created a modem terminal program for the Atari (FlickerTerm80) which uses 40×24 text mode, combined with two character sets with an identical 4×8 font — one with the pixels on the left half of the 8×8 grid, the other on the right. By altering where in memory ANTIC looks for graphics, and which font to display, an 80×24 character screen can be displayed. It uses less memory (about 2KB) and can be more quickly manipulated, compared to rendering 80×24 characters using a 320×192 bitmap mode (which would require about 8KB).

In 1998, Bill Kendrick created a puzzle video game for the Atari (Gem Drop) which utilized a similar effect, but by using two alternating character sets (fonts) in colored text. (Each character is 4×8 pixels, each pixel being one of 4 colors.) No color palette changes occurred, and ANTIC’s Display List wasn’t altered — only a vertical blank interrupt was used to change the character set. This allowed for approximately 13 colors on the screen. Solid color fields that were based on two actual colors (e.g., dark red created by flickering between red and black) had less artifacting because they could be drawn in a checkerboard fashion. This mode was called SuperIRG. (Normal 4×8 multi-colored text on the Atari is called IRG.)

In 1996, Atari demo coders HARD Software from Hungary created HARD Interlacing Picture (HIP), which can display 160×192 pixels in 30 shades of grey. It interlaces two modes — 80×192 with 16 shades of grey, 80×192 with 9 paletted colors — and utilizes a bug in the GTIA chip that causes one of the modes to be shifted 1/2 pixel, allowing for a perceived 160 pixels across.

Later, other demo coders created RIP graphics mode, which is similar to HIP, but can display 160×192 pixels in color.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article “Atari 8-bit family”.

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