written by Matthew Reed

M-ZAL advertisement from 80 Micro

Computer Applications Unlimited advertisement from the December 1982 issue of 80 Micro

M-ZAL was a powerful disk-based editor assembler system for the TRS-80 Model I and III. First introduced in 1981, M-ZAL (which stood for Modular Z80 Assembly Language) was written by Jeffrey Krantz and David Willen. It was sold by Computer Applications Unlimited (also known as CUA) for the price of $149.95.

Although expensive, M‑ZAL was one of the most advanced assemblers ever written for the TRS-80 and it was used by many professional TRS-80 developers. The advertisements contained endorsements from several TRS-80 authors, including:

  • William Denman of MED Systems (co-author of Deathmaze 5000 and Asylum)
  • Chuck Tesler of Prosoft (co-author of Newscript and Allwrite)
  • William Demas (author of Panik and Forbidden Planet)

In addition to M-ZAL, Computer Applications Unlimited sold other TRS-80 development tools. These included XBUG, a $19.95 debugging tool and monitor, and T-ZAL, a $49.95 stripped down version of M-ZAL for cassette users. Unlike M-ZAL, T-ZAL was only available for the Model III.

The M-ZAL package itself consisted of three programs:

  • TXEDIT: “a full screen general purpose text editor which you will use to create, modify, examine, print and merge disk files containing ASCII text.”
  • ASMBLR: “a menu-driver assembler which accepts as input disk files created by TXEDIT and containing assembly language source programs.”
  • LINKER: “an interactive program that you will use to relocate and link together independently assembled program modules.”

Release 2 of M-ZAL, introduced in 1982, added a fourth program named LEXCONV to “facilitate conversion between the various source file formats used by TRS-80 assemblers.” Other important features added to Release 2 included conditional assembly and macros. Release 2 was the most popular and widely used version of M-ZAL.

M-ZAL Release 3 was introduced in 1983. According to the advertisements, the new version added a labeling disassembler, the XBUG-II debugger/monitor, and new linker overlay features. The price was also lowered to $99.95.

In 1984, Micro-Systems Software began bundling a special Model 4 version of M-ZAL with their Model 4 DOSPLUS operating system. It is unclear if this Model 4 version of M-ZAL was also sold separately from DOSPLUS.

David Willen and Jeffrey Krantz later wrote the well-regarded book 8088 Assembler Language Programming: The IBM PC. But they don’t appear to have ever written a version of M‑ZAL for the IBM PC.

Categories: Programming, Software


Greg says:

I really liked M-ZAL I spent many hours working with it. Still my favorite development tool.

Jerry Kaidor says:

I used M-Zal extensively. I had built a serial port and a modem for my Model I, hoping to participate on computer bulletin boards. To my shock and dismay, Radio Shack’s modem program didn’t work with my hardware ( duhhhh ). So I wrote a modem program in Z80-ASM using M-ZAL. I used multiple files, macros, conditional assembly – pretty much everything. The stuff I learned led to a 20 year career in software engineering.