AltairDrive

BitsBy8

BitsBy8 turns a Raspberry Pi (or any Linux/macOS machine) into a disk server and virtual-machine workbench for the MITS Altair 8800 and other S-100 computers.

It serves virtual floppy and hard-disk images to a real Altair through its FDC+ Enhanced Floppy Disk Controller over a serial cable — and it can also build and boot fully virtual S-100 machines right in your browser, no hardware required. Everything runs from a single Svelte web UI, with a REST API and an MCP server for AI assistants on the side.

Version: 3.0.0-alpha · License: GPL-3.0 · Platforms: Linux (Raspberry Pi & x86), macOS

Note: BitsBy8 is the product name. The Debian package and systemd service are now named bitsby8 (the CLI is bitsby8, with an fdcsds alias kept for backward compatibility). The source repo is still fdcplus-web.

What it does

Serve disks to a real Altair. Mount up to four floppies (plus larger hard-disk images) and serve them to an unmodified Altair 8800 through its FDC+ controller over serial — or over a WebSocket link to an Altair simulator. Drives can be read-only or copy-on-write, and multiple machines can share the same library at once.

Run virtual machines. Assemble an S-100 computer from a catalog of emulated cards — CPU (8080/Z80), RAM, disk, serial, video — save it as a reusable Machine Profile, and boot it in the browser. Each running machine gets a live serial console, an Altair-style front panel, and a video monitor (VDM-1 character display / Cromemco Dazzler graphics). Snapshot a machine and restore it later.

One place to drive it all. The web UI, a full REST API, and an MCP server (90+ tools) all reach the same live state, so you can operate BitsBy8 by hand, from scripts, or from an AI assistant.

At a glance:

• 💾 Disk serving over real serial or WebSocket, with read-only and copy-on-write (transient / per-client "splinter") mounts you can keep, commit, or save as a new image
• 🖥️ Virtual S-100 machines — card catalog, machine profiles, and a run cockpit with console, front panel, and video monitor
• ⌨️ VT102 terminal in the browser for a real serial console or a virtual machine's console — reconnects where you left off
• 🧑‍🤝‍🧑 Multi-client serving so several machines (real and virtual) share one disk library
• 📼 Cassette audio playback
• 🤖 AI assistant integration via MCP (stdio or HTTP), plus OpenAPI/Swagger docs at /api/docs

Quick start (no hardware needed)

Try the whole thing on your laptop — mount a sample disk or boot a virtual machine without an Altair in sight:

git clone <repo-url> fdcplus-web && cd fdcplus-web
pnpm install            # provisions the backend + frontend workspace
pnpm dev:all            # backend + web UI, live-reloading
open http://localhost:3000

Requires Node.js 22+ and pnpm.

Installation

Raspberry Pi / Debian (recommended for real hardware)

Build and install the .deb, then run it as a systemd service:

make deb
sudo dpkg -i ../bitsby8_*.deb
sudo apt-get install -f            # pull in any missing dependencies

sudo nano /etc/bitsby8/bitsby8.config.json   # set your serial port, drives, etc.
sudo systemctl enable --now bitsby8          # start on boot and now

Upgrading from an older fdcsds install is automatic — apt supersedes it and your config, data, and database are migrated.

The web UI is then at http://<pi-hostname>:3000. See DEBIAN-PACKAGE.md for the full packaging guide.

Docker

docker compose up -d      # then open the web UI (default port 3000)

Configuration and data persist in the mounted volume; see docker-compose.yml.

From source

git clone <repo-url> fdcplus-web && cd fdcplus-web
pnpm install
pnpm build:all            # compile backend + build the web UI
pnpm start -- --web       # or: bitsby8 --web  (if installed globally)

Connecting a real Altair

Wire the FDC+ controller to a USB serial adapter and point BitsBy8 at that port:

bitsby8 -p /dev/ttyUSB0 -0 disks/cpm22.dsk -w
# -p  serial port for the FDC+     -0..-3  mount a disk to a drive
# -w  enable the web interface     -b <rate>  set baud (default 230400)

A second serial port can drive an interactive console terminal in the web UI:

bitsby8 -p /dev/ttyUSB0 -0 disks/cpm22.dsk \
  --terminal-port /dev/ttyUSB1 --terminal-baud 9600 -w

A few setup notes:

• Serial permissions (Linux): add your user to the dialout group (sudo usermod -aG dialout $USER, then log out and back in).
• Stable port names: USB port names like /dev/ttyUSB0 can shuffle across reboots. Run bitsby8 --show-persistent-paths to get a stable /dev/serial/by-id/... path for your config.
• No physical FDC+? An Altair simulator can connect over WebSocket instead of serial — see docs/WS-FDC-TRANSPORT.md.

Generate a starter config any time with bitsby8 --example-config > .bitsby8.config, and run bitsby8 --help for the full option list.

The web interface

Open the UI and everything is in the left sidebar:

More detail in docs/WEB-INTERFACE.md.

AI assistant integration (MCP)

BitsBy8 ships a Model Context Protocol server exposing 90+ tools — mount disks, drive machines, read/write CP/M files, run the terminal — to assistants like Claude Code. It's off by default; opt in per transport:

• Local (stdio): point your assistant at bitsby8 --mcp:

  { "mcpServers": { "bitsby8": { "command": "bitsby8", "args": ["--mcp", "--data-dir", "/path/to/data"] } } }

• Over the LAN (HTTP): set an API key, then enable MCP-over-HTTP in Config → MCP server (or --mcp-http). It requires a bearer token and is intended for trusted networks — put TLS in front if you expose it.

The tools can read and write disk images and send bytes to real hardware, so don't point an assistant at a production machine without meaning to.

Configuration

Settings live at two layers:

• Install-time defaults — a config file (/etc/bitsby8/bitsby8.config.json, or .bitsby8.config from source) plus CLI flags. These set up the box; changes take effect on restart.
• Day-to-day settings — managed live from the web UI (and REST/MCP), stored in a SQLite database in the data directory. Per-image settings like notes, write policy, and snapshots live here and apply immediately.

The data directory (/var/lib/bitsby8 on a .deb install) holds your disk library, uploads, cassettes, and the database.

Documentation

• DEBIAN-PACKAGE.md — building and installing the Debian package
• docs/WEB-INTERFACE.md — web UI walkthrough
• docs/WS-FDC-TRANSPORT.md — WebSocket disk transport for simulators
• docs/PROTOCOL.md — the FDC+ serial disk protocol
• docs/TROUBLESHOOTING.md — common issues
• CONTRIBUTING.md — how to contribute

License

GPL-3.0.

Credits

• BitsBy8 software (disk server, web interface, virtual machines, MCP server): Joe Toppe, 2024–present.
• FDC+ Enhanced Floppy Disk Controller hardware: Mike Douglas / deramp.com. BitsBy8 talks to that controller over serial; the hardware itself is a separate product.

See AUTHORS for the full contributor list.

References

• FDC+ Hardware Documentation
• Altair 8800 (Wikipedia)
• Node.js SerialPort