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The Burroughs B5500 was an innovative computer system. Released first as the B5000 in 1962 and then, with minor improvements and a new disk subsystem, re-released as the B5500 in 1964, its design was a radical departure from other commercial systems of the day. Many of the concepts that it embodied were being worked on and implemented by others around the same time, but it is difficult to think of another system that pulled so many new concepts together and made them work so well in a commercially-successful product:

  • Stack- and descriptor-oriented instruction set
  • Variable-length memory segments
  • Hardware bounds checking
  • Unified integer/floating-point numeric format
  • Designed for and programmed exclusively in higher-level languages
  • Designed for and managed by a sophisticated operating system, the Master Control Program, or MCP
  • Multi-programming (multiple tasks sharing the same processor)
  • Multi-processing (multiple physical processors sharing common memory and I/O)
  • Automatic memory allocation and address relocation
  • Automatic memory segment overlay (what we now call virtual memory)
  • Use of labeled file media and automatic assignment of labeled file media to requesting programs (what we now call automatic volume recognition)

The B5500 was the foundation for the Burroughs B6x00/7x00/A Series systems, which are still produced and sold today as Unisys ClearPath MCP systems.

The main goal of this project is creation of a web browser-based emulator for the B5500. A second goal is reconstruction of source and object code for the system.

A complete software release (Mark XIII, 1971) is presently available from the hosting site below under liberal terms of a Unisys educational/hobbyist license.

The contents of this project are licensed under the MIT License.

Related Sites URL
Getting Started
Project Blog
Web/email Forum
Emulator hosting site
Burroughs Mark XIII Software Release
B5500 at retroComputingTasmania
Documents at
Release Downloads

This project was originally hosted on Google Code at and moved to GitHub in June 2015.


Web-based emulator and operating environment for the Burroughs B5500 computer system.








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