Port 3680: NPDS Tracker — The Ghost Port for a Beloved Dead Computer

Port 3680 is registered to the NPDS Tracker — Newton Personal Data Sharing Tracker — a service for discovering and listing active web servers running on Apple Newton devices.¹

Apple discontinued the Newton in 1998. This port was registered in 2003. The tracker is still running.

What NPDS Is

NPDS (Newton Personal Data Sharing) is a lightweight HTTP server that runs on Apple Newton MessagePad and eMate devices. It turns your PDA into a web server you can hold in your hand — serving pages, sharing contacts, exposing data over HTTP from a device running Newton OS 2.x.²

The tracker at port 3680 is the registry that makes it all discoverable. Newton devices running NPDS register themselves with a tracker server. The tracker validates them periodically, maintains a live list of active servers, and allows trackers to share their registrations with each other. It's a small federated directory of web servers running on 1990s hardware.³

The tracker server was originally developed by Victor Rehorst and Paul Guyot. The NPDS project itself grew from code by Matt Vaughn, based on sample code from Ray Rischpater.²

The IANA Registration

IANA formally registered port 3680 to npds-tracker in January 2003 — five years after Apple killed the Newton.¹ Both TCP and UDP are registered.

This is what IANA registration actually means: a community asked for an official port number, demonstrated a real implementation, and received it. The port doesn't become more or less useful because of the registration. It just means port 3680 is set aside, in perpetuity, for Newton tracker servers.

Who Is Still Using It

The Newton enthusiast community. There's a small, dedicated group of people who still run Newton hardware, write Newton software, and maintain infrastructure like the NPDS tracker. As of late 2025, the NPDS site is actively maintained and tracker servers remain online.²

If you're running a Newton and you want your web server to be discoverable, port 3680 is where you announce yourself to the world.

What You'll Actually Find on Port 3680

Almost certainly nothing. Unless you're running an NPDS tracker server, nothing should be listening here. If something is, check it — it may be an application that chose this port arbitrarily, which is common with registered ports that serve obscure or historical protocols.

How to Check What's Using Port 3680

# macOS / Linux: show what process is listening on port 3680
sudo lsof -i :3680

# Linux alternative
ss -tlnp | grep 3680

# Windows
netstat -ano | findstr :3680

If the output is empty, nothing is listening. That's the expected result on nearly every machine in the world.

Why This Port Exists

Registered ports (1024-49151) exist for exactly this kind of use: a protocol with a real implementation, a real community, and a need for a stable, consistent port number. The IANA doesn't evaluate whether a technology will succeed commercially or survive into the future. It allocates port numbers. Port 3680 will be registered to Newton tracker servers for as long as the port number system exists.

The Newton died in 1998. Its port registration is immortal.