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RSX180[1] is a multi-tasking, multi-user, multi-terminal Operating System for the Zilog Z80 family of processors that is similar in both look and feel and design philosophy to DEC's RSX-11M OS for the PDP-11 series of machines.

The system was written as a hobby project back in the early 80s for the Intel 8080 CPU. It started life as a micro-kernel with a fixed number of tasks, but later grew to support dynamic tasks, a custom RAM-disk-based filesystem, device drivers, a CLI, and a very basic set of utilities. The system design was heavily influenced by RSX-11M, which was a popular multi-tasking OS at the time.

Most of the original 8080 code was lost after the project was abandoned, but part of the kernel was found in the early 2010s and ported to the P112 CPU board, which has a Z80182 CPU with built-in MMU. Many bugs were fixed in the process, the filesystem upgraded to make use of floppy and hard disk storage, memory management improved, and the utility programs were written again from scratch.


  • Multi-user
  • Multi-terminal
  • Priority-based, preemptive multitasking micro-kernel
  • Round-robin scheduling of tasks of the same priority
  • Custom two-level filesystem[2]
  • Modular device drivers
  • QIO mechanism
  • AST support
  • Event flags
  • Dynamic allocation of system resources
  • Send-Receive task communication mechanism
  • Kernel functionality extended by privileged tasks
  • Task Directory for fast task activation.
  • Tasks can be fixed in memory for even faster activation.
  • Clock queue and time-scheduled task execution.
  • Privileged and non-privileged users.
  • CLI similar to MCR[3]
  • Fits on a single 1.44 MB floppy

Current status[edit]


  1. "P112 Support Page". - Main RSX180 page at SourceForge
  2. - VOL180 Filesystem Specification
  3. "P112 Support Page". - Using RSX180

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