Tandy Graphics Adapter

When IBM designed the PCjr, they corrected several oversights made with the original CGA standard. The 160x100x16, 160x200x16, 320x200x16, modes where now fully documented features that did not require hacks and worked with RGB monitors. A 640x200x4 mode was also added. When Tandy cloned the PCjr design, they initially made some minor improvements as well. Games could be made to look a bit better on Tandy than PCjr while being fully compatible with both. The PCjr of course was canceled and Tandy made minor alterations to create what they cautiously termed an "MS-DOS compatible" computer (not "IBM-PC compatible"). This was an inadvertently modest claim as it turned out their hardware had more widespread compatibility with IBM-PC software than IBM machines for many years to come. Game developers eagerly supported the Tandy hardware with boxed Tandy versions of their games, including Tandy executables with their IBM-PC games, or made a game that could be configured to run with improvements on Tandy hardware. A single version configurable for Tandy graphics eventually became the standard practice.

CGA was notorious for having only 4 colors and 2 eye-straining palettes (technically not quite that bad, but actually that bad in real world use). Unlike IBM-PC video standards, Tandy graphics allowed any of 16 colors to be chosen for 1-bit, 2-bit, and 4-bit color modes. Fully documented, no hacks required. IBM actually cloned Tandy's programmable palette when defining the EGA standard.

All IBM-PC video standards (including PCjr) use dedicated Video RAM. The Tandy video hardware shares the main memory system RAM. This allows for double and triple buffering, or even 7 fold buffering. Where CGA was practically limited to 30 FPS for any graphic, Tandy was only limited by the refresh rate of monitor (60 FPS in its lifetime). Some DOS games pushed to 60 and 70 FPS but this strained the system and sometimes resulted in graphic errors such as tearing (and those were SVGA, not CGA or EGA!). Full screen at 60 frames, while possible, did not necessarily represent the best use of Tandy graphics since CPU and RAM speeds were not near that level. The high frame rate capability was used to deliver very smooth animation of game characters on screen. It also allows cartridges to have direct access to the video's RAM. And developers could write a game to use any screen resolution they wanted if they so chose, such as 720x255 (completely backwards compatible with older Tandy monitors) or 720x350 (again, other IBM-PCs and compatibles would have to wait for SVGA for such features). Also, a software sprite engine could make use of the shared video RAM and get much better performance than a software sprite engine for other IBM-PC video hardware.

Reaching nearly a 10% market share at the height of their popularity, Tandy even continued to expand their graphics hardware with confidence that game developers would use the added features. They did. "Tandy Video II" or "ETGA" added a 256 color palette (undocumented) and 640x200x16 mode (documented). Developers were able to coax 640x200x256 mode out of it also. Game developers showed a remarkable level of loyalty to their Tandy customers going so far as to modify EGA games to display correctly on ETGA hardware and there was even a driver created to directly play an EGA mode game on ETGA. While it was made for a single game, the TGA640C.DRV file can be substituted for the EGA640.DRV file from any game that uses it. That may not seem remarkable, but consider that at this point Tandy users could plug any 8-bit and some 16-bit video cards into their machines and play most any DOS game in its full intended color using standard IBM-PC video modes. Tandy added hardware to to save money for their customers, game developers took the time to do the same.