Heath-Zenith Z-120
[Vin90]
The Heath-Zenith Z-120, introduced in 1982, was a notable all-in-one personal computer featuring both 8-bit (8085) and 16-bit (8088) processors, allowing it to run both CP/M and MS-DOS software a rare hybrid design for its era. Its claim to fame was its expandability with an S-100 bus, robust all-in-one build with an integrated CRT, and popularity among universities and the U.S. military for training and academic use, making it one of the few S-100 systems to achieve significant production and institutional adoption.
- Manufacturer: Zenith Data Systems
- Release Date: 1982
- Cost at release: USD $2,995 (CAD ~$11,750 adjusted for inflation)
- MIPS: 0.37-0.8 (370-800 KIPS) – depending which processor is used
Hardware Specifications
- CPU: Dual CPUs – Intel 8085 (8-bit) and Intel 8088 (16-bit), switchable depending on software needs.
- RAM:
- Standard: 128 KB, expandable to 192 KB on-board.
- Maximum: Up to 768 KB with S-100 expansion cards.
- Expansion: Five S-100 (IEEE-696) slots for expansion boards and peripherals.
- Storage:
- Two 320 KB (40-track, double-sided) 5.25-inch floppy disk drives (internal).
- Support for external 8-inch floppy disk drives.
- Some configurations supported hard drive expansion.
- Display:
- Built-in monochrome CRT (12-inch).
- Monochrome display upgradable to 8 greyscales.
- High-resolution bitmap graphics: up to 640×225 pixels; color systems could display 8 colors (RGB).
- Ports:
- Two serial ports (RS-232).
- One parallel port (Centronics-compatible).
- Keyboard: Built-in, based on IBM Selectric layout.
- Weight: Approximately 55 pounds (packed shipping weight)
Operating System & Programming Languages
- Operating System:
- Z-DOS (Zenith MS-DOS-compatible): A non-IBM compatible version of MS-DOS, often referred to as Z-DOS, was the primary 16-bit operating system. It allowed the machine to run a variety of business and productivity software developed for early MS-DOS environments.
- CP/M-85: Leveraging the 8-bit 8085 CPU, CP/M-85 was available for running a rich catalog of 8-bit business and development software.
- CP/M-86 and Concurrent CP/M-86: Supported as alternative 16-bit operating systems for more advanced or multitasking needs.
- H-DOS, UCSD Pascal, and others: The system also ran Heath’s own HDOS and niche operating environments such as UCSD Pascal, popular with universities for structured programming instruction.
- Supported Languages:
- Microsoft BASIC (BASIC-80 for CP/M-80, Z-BASIC for Z-DOS)
- Microsoft FORTRAN-86 (for Z-DOS)
- Microsoft COBOL-86 (for Z-DOS)
- Microsoft Pascal (for both CP/M and Z-DOS)
- Microsoft BASCOM-86 (for Z-DOS)
- Assembly language (with available assemblers and editors for CP/M and Z-DOS environments)
- UCSD Pascal and other languages available for CP/M systems
Notables
- Dual-Processor Hybrid: One of the first personal computers with both 8-bit (8085) and 16-bit (8088) CPUs, letting users run both CP/M and MS-DOS software—bridging two computing generations.
- S-100 Bus Expansion: Unusually, it offered S-100 bus slots, supporting robust hardware upgrades and hobbyist modifications even as the industry shifted to different bus architectures.
- Superior Graphics: Had advanced graphics for its era, supporting high-resolution bitmap and more colors/greyscales than many early IBM-compatible PCs; early versions of AutoCAD were developed for it for this reason.
- All-in-One, Robust Build: The Z-120 “all-in-one” design included an integrated monitor and rugged construction; known for its reliability in universities and demanding military environments.
- In 1983, Clarkson University became the first U.S. college to provide a personal computer to each incoming freshman—the model was the Z-100 family (including the Z-120).
- Widely adopted by the U.S. military for training and office use due to its solid build and flexibility.
- Partial Compatibility: Dubbed a “near-compatible” with IBM PC—generic MS-DOS software typically worked, but popular programs that used IBM-specific BIOS extensions often did not, resulting in a unique niche and loyal user base.
- Kit & Ready-Built Versions: Available as a Heathkit for enthusiasts to assemble themselves, or fully pre-built by Zenith Data Systems for institutions and businesses.
- Among the first all-in-one systems to blend 8-bit and 16-bit computing in a single package
Donated by: Arlen Michaels