We know the TI-99 and Tomy Tutor are related. We just don’t know how.


The TI-99/4A arrived in 1981. Tomy introduced the Pyuuta (ぴゅう太) in Japan in 1982, followed by the American Tomy Tutor in 1983. They came from different companies, served different markets, and belonged to separate software ecosystems.

Yet they share one wonderfully misleading physical detail: a TI-99 cartridge fits perfectly into the Tutor’s cartridge slot—even though the electrical pinout is completely different. Mechanically compatible, electrically incompatible.

The connection goes much deeper than the cartridge shell.

In 2020, AtariAge user KL99 (Klaus Lukaschek) turned a community disassembly thread into a public investigation of the Tutor’s software ancestry. He did more than identify similar commands or programming style: he adapted preserved TI Extended BASIC source files to assemble at the Tutor’s memory locations, removed the portions that were absent from the Tomy implementation, and compared the resulting binary directly against the Tutor ROM.

The result was a continuous match from addresses >9029 through >B90F: approximately 10.5 KiB of Tutor BASIC reconstructed from minimally modified TI Extended BASIC source code. That provides reproducible evidence of direct code ancestry between the two systems, although it does not answer whether the code was licensed, transferred through a development partner, or obtained through some other arrangement.

KL99 also recorded a video presentation explaining the discovery. Its current location has not yet been recovered; when found, it will be linked here alongside the original thread and source comparison.

What we still do not know is how that relationship happened.

No internal Tomy Japan engineering records, source archives, licensing agreements, or design documents are publicly available. What appeared to be a collection of original Pyuuta development documentation surfaced once in a Japanese auction, but the winning bidder never released it. Until those records reappear, the exact path from Texas Instruments to Tomy remains an intriguing gap in computer history.

We know the machines are related. We can prove that they share both architectural ideas and software ancestry. What we cannot yet prove is whether Tomy licensed TI technology, collaborated with TI or one of its partners, inherited an abandoned design path, or arrived at the final machine through some other arrangement.

That mystery is part of what makes this project so compelling.

Hardware background


The relationship is visible in the silicon:

  • The TI-99/4A uses a TMS9900 processor, TMS9918-family video, and TI sound hardware.
  • The Tomy Tutor/Pyuuta uses the closely related TMS9995 processor, a TMS9918-family video processor, and an SN76489-family sound generator.

These are not identical computers, but they speak closely related hardware dialects.

That similarity creates an unusual opportunity: instead of emulating an entire TI-99/4A, could we rebuild only the missing environment and allow TI software to run through the Tutor’s real CPU, video, and sound hardware?

The answer became Tutor TI Compatibility 3.0.

It is a 16 KiB replacement BIOS that bridges the differences in firmware, memory layout, cartridge services, GPL execution, keyboard and joystick input, video access, sound, and timing—allowing selected TI-99/4A cartridges to cross onto a real Tomy Tutor/Pyuuta.

This is not a complete TI-99 emulator. The idea is to reuse everything the machines genuinely have in common and translate only the parts that differ.

Watch the TI Demonstration running on physical hardware:

https://www.youtube.com/watch?v=G_nsBboMJFg

The hardware trick

Two boards form a matched system:

  • The ESE Game Adapter, made by Takeo Namiki, is set to 2/16, replaces the Tutor system BIOS with a fixed 16 KiB compatibility core at CPU addresses >0000–>3FFF.
  • The...
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