Emulating the Z-100 Computer

This poster presents the first working emulator of the Zenith Z-100 personal computer. The Z-100 was released by Zenith Data Systems and Heathkit in 1982. Although it was contemporary with IBM's 5150, the ancestor of modern PCs, it is not PC-compatible, and Z-100 software can only run on that computer. Due to the dwindling number of extent Z-100s, and the absence until now of any emulator to run Z-100 programs, a vast corpus of Z-100 data is irretrievable.

Despite similarities to the PC, such as the same processor and a variant of Microsoft DOS ("Z-DOS"), the Z-100 had many idiosyncrasies, including memory-mapped video, a second processor, and its own BIOS, ports, and interrupts. Its video, highly advanced for the time, led to its adoption by the US Air Force and Clarkson University [3]. Much creative work was developed on this computer, including games, utilities, documents, spreadsheets, and blueprints. Z-100 disks can be read by a modern PC with a 5 1/4" drive; however, Z-100 programs will not run on a PC or existing emulator, and word-processing save files, BASIC files, and spreadsheets are saved in compressed, proprietary formats unreadable without their original programs.

Our Z-100 emulator, posted publicly [1], models all of the system necessary to boot Z-DOS and run many Z-100 programs. We modeled the processors, glue logic, video, and the wrote the first timing-accurate simulation of the WD1797 floppy controller. We tested using a monitor ROM and floppy disk images from a Z-100 in our possession. Our emulator runs Z-DOS, most of the Z-DOS core utilities, the GALAHAD word processor, the Multiplan spreadsheet program, and Z-BASIC. We tested disk images containing BASIC games, spreadsheets, and word documents, all saved in proprietary formats previously unreadable. Our emulated programs opened all these data files successfully and allowed us to extract them to text files.

[1] http://www.github.com/mdblack/Zenith-Z-100

[2] Matta, "A Zenith Z-100 Emulator", MS Thesis, Bridgewater State University, 2021.

[3] "Clarkson College to Issue Computers to Student Body". Silicon Gulch Gazette. February 1983.

[4] "Zenith Z-100 Technical Manual", Zenith Data Systems, 1982.