WHAT IS TEZXAS?
The very first opinion is that Tezxas is misspelled word Texas. Not exactly.
TI 89 is a new machine. Although software for it grows rapidly, it still can not be compared with software base for older computers. And, while on desktop area incompatibility vanished (you have PC with some operating systems or Macintosh with MacOS), every calculator, even from the same producer is still own story.
But, before PC-mania existed many other computers: Apple II, TRS 80, ZX81, ZX Spectrum, CP/M computers, Sinclair QL, BBC-B, Commodore 64, Amstrad CPC 464, Oric Atmos, Atari 520 ST, Commodore Amiga ... All of them had their own software.
My first computer was ZX Spectrum. I bought it in 1984. The characteristics seem today funny: 48 kilobytes of RAM, tape recorder as memory unit, CPU Z80 at 3.5 MHz, graphic 256x192 pixels in 16 color (group of 64 pixels must be in one of two colors), beeper sound generated by CPU, rubber keyboard ...
But, such machine was ideal for introduction to computers world. With start price of 100 GBP, it was enough cheap even for East Europe, or Latin America. Unlike it major opponent Commodore 64 , wich was better machine for users of commercial games and utility programs, ZX Spectrum had BASIC ideal for easy writing your own software. Soon appeared a dozens of commercial and freeware games, programming languages, word processors, spreadsheets ... My estimation is that there were about 20000 programs (including those published in newspapers all over the world). Today on Internet there are about 8000 available programs for ZX Spectrum.
The software for ZX Spectrum after 1986 was reduced to games, and in 1992 even games stopped with releasing.
My later computers were Casio fx-8000, AT-286, 486-SX, Pentium 100 and TI-89, but ZX Spectrum was my first love.
Well, starting from 1990, Spectrum moved to virtual computer. Almost everyone replaced ZX Spectrum with PC, Amiga or Atari ST, but those machines were enough powerful to execute emulators at machine code level. First emulators were written, and interest for ZX Spectrum reappeared. The games are now written for emulated Spectrums, and in Russia the modernized versions of ZX Spectrum are still produced.
Zeljko and me wrote one excelent emulator of ZX Spectrum for MS DOS computers. It is called Warajevo ZX Spectrum emulator because it was written mainly in Sarajevo during Bosnian war.
OK, OK, Stop with history, What is TeZXas?
The same day I have bought TI-89 I started to write ZX Spectrum emulator for it. It was a challenge, this was my first TI-89 program, and first Motorola 68000 assembly program! And, I was limited to 10 MHz machine with only 180 KB available memory and small screen.
The result of symbiosys of Texas Instruments TI 89 and Sinclair ZX Spectrum is Tezxas, the emulator. Now, TI89 can start almost all games originally written for ZX Spectrum.
Later I ported Tezxas to TI92+. The bigger screen was big advantage.
Tezxas is not perfect emulator. Some games are slow, screen is sometimes hardly visible, keyboard layout is strange. But keep in mind that TI89 is the most limited machine that emulates ZX Spectrum 48K at machine code level, and that perfomances of Tezxas are better than perfomances of some emulators on Pentium 133.