What’s worse, is that the TRS-80’s clock speed is similar to that of the Altair (in contrast to the power of the PDP-10), so the TRS-80 emulator would be considerably slower than the real machine. I hadn’t any previous experience with emulation, and while the 8080’s instruction set is compatible to the Z80’s, I quickly discovered it would take many instructions by the Z80 to emulate an 8080 instruction. I wouldn’t go as far as depicting the Altair’s front panel of flashing lights as other emulators do, but would expect the BASIC to run & ultimately run any Altair BASIC program. I would write in Z80 assembly language an 8080/Altair emulator that would execute 4K BASIC in high memory of the TRS-80. My idea was to use my Model III where Allen used a PDP-10. Gates & Allen were able to write their BASIC interpreter without using a real 8080 microprocessor CPU, then load it into a real Altair, whereby it ran faultlessly. He had previously used a PDP-10 to emulate the much lesser 8008 CPU. The Altair (image sourced from )Īs Gates & Allen didn’t possess the recently released Intel 8080 CPU, let alone a developer’s kit for such a device, Allen set about emulating the 8080 machine instructions on a PDP-10 minicomputer. The history is well known whereby in 1975 Bill Gates, Paul Allen & Monte Davidoff created Altair 4K BASIC to run on the newly developed microcomputer – the Altair – produced by MITS of Albuquerque, USA.įigure 1. While reading Paul Allen’s book Idea Man, I had the idea to create an emulator of the 8080 Altair on my TRS-80 Model III. I've given Philip this web space to make the emulator available to those who might want to check it out. He's recently exercised his mind creating an Altair emulator for the venerable TRS-80 Model III. Terry Stewart's (Tezza's) Projects and Articles (Blog) Blog index and site links An Altair Emulator for the TRS-80 Model IIIĪssembly language aficionado Philip Avery is a long time TRS-80 user who has a keen interest in vintage computers.