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Color Computer 3 (1986–1991)
On July 30, 1986, Tandy announced the Color Computer 3 at the Waldorf-Astoria Hotel in New York City. It came with 128K of RAM, which could be upgraded to 512K. The keyboard surround and cartridge door plastic were changed from black to grey. The keyboard layout was revised, putting the arrow keys in a diamond configuration and adding CTRL, ALT, F1 and F2 keys. It sold in Radio Shack stores and Tandy Computer Centers for $219.95.
The CoCo 3 was compatible with most of the CoCo 2’s peripherals. Most older software ran on it. Taking the place of the graphics and memory hardware in the CoCo 1 and 2 was an application-specific integrated circuit (ASIC) called the “GIME” (Graphics Interrupt Memory Enhancement) chip. The GIME also provided additional features:
- Output to a composite video monitor or analog RGB monitor, in addition to the CoCo 1 and 2’s TV output. This did much to improve the clarity of its output.
- A paged memory management unit which broke up the 6809’s 64k address space into 8x8K chunks. Although these chunks were considered to be too large by many programmers, the scheme would later allow third party RAM upgrades of up to 2 MB (256x8k).
- Text display with real lowercase at 32, 40, 64, or 80 characters per line and between 16 and 24 lines per screen.
- Text character attributes, including 8 foreground and 8 background colors, underline, and blink.
- New graphics resolutions of 160, 256, 320 or 640 pixels wide by 192 to 225 lines.
- Up to 16 simultaneous colors out of a palette of 64 displayable at one time (unless programming tricks were employed to display more).
Omitted from the GIME were the seldom-used SAM-created Semigraphics 8, 12, and 24 modes. A rumored 256 color mode (detailed in the original Tandy spec for the GIME) has never been found.
Previous versions of the CoCo ROM had been licensed from Microsoft, but by this time Microsoft was not interested in extending the code further. Instead, Microware provided extensions to Extended Color BASIC to support the new display modes. In order to not violate the spirit of the licensing agreement between Microsoft and Tandy, Microsoft’s unmodified BASIC software was loaded in the CoCo 3’s ROM. Upon startup, the ROM is copied to RAM and then patched by Microware’s code. Although this was a clever way of adding features to BASIC, it was not without some flaws: the patched code had several bugs, and support for many of the new hardware features was incomplete.
Microware also provided a version of the OS-9 Level 2 operating system shortly after launch. This OS featured memory-mapping (so each process had its own memory space up to 64K), windowed display, and a more extensive development environment that included a bundled copy of BASIC09. C and Pascal compilers were available. Various members of the CoCo OS-9 community enhanced OS-9 Level 2 for the CoCo 3 at Tandy’s request, but Tandy stopped production of the CoCo 3 before the upgrade was officially released. Most of the improvements made it into NitrOS-9, a major rewrite of OS-9/6809 Level 2 for the CoCo 3 to take advantage of the added features and speed of the Hitachi 6309 (if the unit has the Hitachi CPU installed).
The 6809 in the CoCo 1 and 2 ran at 0.895 MHz; the CoCo 3 runs at that frequency by default, but is software controllable to run at twice that rate; OS-9 takes advantage of that capability. Some models of CoCo 1 and 2 were also capable of running at this higher speed, but this was not supported or guaranteed.
A popular accessory was a high-resolution joystick adapter designed by CoCo enthusiast Steve Bjork. While it did increase the resolution of the joystick/mouse interface by a factor of ten, it did so at the expense of CPU time. A modified version of this interface was included with a software package by Colorware called CoCo-Max 3, by Dave Stamp. This was a MacPaint work-alike but added support for color graphics. This was a very desirable product for CoCo owners and combined with a MacWrite-like word processor called MAX-10 (also by Dave Stamp and internally named “MaxWrite”), provided much of the functionality of an Apple Macintosh, but with color graphics and at a fraction of the cost.
While the CoCo 3 featured many enhancements and was well received, it was not without problems and disappointments. As initially conceived, the CoCo 3 had much hardware acceleration and enhanced sound. However, internal politics crippled the design so it would not be perceived as a threat to the Tandy 1000. This again limited the platform’s potential as a game console. Early versions of the GIME had DRAM timing issues which caused random freezes. Due to bugs in the GIME some features that were problematic were marked as “reserved” or “do not use” in the programming and service manuals.
The power supply was marginal, and some would overheat if the system memory was expanded to the full 512K capacity. Some CoCo 3 owners opted to add a small fan inside the case to keep it cool.