The MITS Altair 8800, and the bus it was built on
A C++20 simulator of the Altair 8800 and the S-100 bus — with a command monitor, a full symbolic debugger, and a built-in MCP server so an AI assistant can drive the machine directly. It boots period software unmodified, and it is a bench for building new hardware as well.
A monitor worth living in
A command prompt with line editing and history. Build the
machine live with BOARDS ADD, configure it with
SET and SHOW, mount disks and tapes, and save
the whole thing back out as a TOML file.
A real symbolic debugger
Conditional breakpoints and tracepoints, single-step over calls,
annotated disassembly, and symbols loaded from a period
.PRN listing. HISTORY is a flight recorder:
a crash is something you rewind into, not something you reproduce.
Built-in MCP server
altairsim --mcp exposes the machine as typed, structured
tools, so Claude drives it properly instead of screen-scraping a
terminal. It runs on the same machine object the monitor does —
not a wrapper, not a second model of the world.
The S-100 bus, modeled
Forty-odd board types — MITS, Cromemco, Processor Technology, SD Systems, iCOM, Tarbell, North Star, CompuPro — each built from its own manual, each chip from its datasheet. Boards respond to bus cycles, so DMA and vectored interrupts fall out rather than being bolted on.
Period software, unmodified
Altair 4K and 8K BASIC off cassette, CP/M 2.2 on 8″ and 5¼″ floppies, CP/M 3 on CompactFlash and SD, Cromemco CDOS, SD Systems SDOS, iCOM FDOS, North Star DOS and MITS Programming System II. Sound boards play through your speakers. More than thirty ready-built machines are in the binary.
Nothing to install
Pre-built, self-contained packages for Linux, Windows and macOS (Apple Silicon and Intel). Building it yourself needs only a C++20 compiler and CMake — there are no dependencies to fetch. SDL3 is detected, never required.
Getting started
Take a build from the downloads area — there is nothing to install — and the User Manual will bring up a first machine and boot CP/M. The debugger guide covers breakpoints, tracing and symbols; the Developer Guide walks through adding a board of your own. There is more about the project, and the source is on GitHub.