Port 1374: Molly — The MBE control port you'll probably never see

Port 1374 is a registered port assigned to a service called "molly," developed by EPI Software Systems. If you've never heard of it, you're not alone. This port exists for a genuinely niche purpose: controlling molecular beam epitaxy (MBE) systems used in semiconductor and materials research.¹²

What Is Molly?

Molly is growth control and scheduling software for MBE equipment. Molecular beam epitaxy is a process for growing ultra-thin crystalline layers of semiconductors—one atomic layer at a time. It's used in research labs and specialized manufacturing to create structures for quantum devices, lasers, and advanced electronics.

The software uses port 1374 (both TCP and UDP) to communicate with process control hardware, coordinate growth schedules, and manage the equipment.³

The Registered Port Range

Port 1374 falls in the registered port range (1024–49151). This range is managed by IANA, which assigns ports to specific applications and services upon request. Unlike well-known ports (0–1023) that require root privileges, registered ports can be used by user-level processes.

EPI Software Systems registered port 1374 for molly, meaning it has an official designation—but that doesn't mean it's commonly used. Most registered ports serve specialized applications that only appear in specific environments.

Will You Ever See This Port in Use?

Probably not.

Unless you work in a semiconductor research lab or materials science facility with MBE equipment, port 1374 will sit dormant on your system. The service is designed for local area network (LAN) communication between control computers and scientific equipment, not for Internet-facing services.⁴

This is one of those ports that exists in the registry because someone, somewhere, needed a standardized way to talk to very expensive, very specialized machines.

Checking for Activity on Port 1374

If you want to see whether anything is listening on port 1374 on your system:

On Linux or macOS:

sudo lsof -i :1374

On Windows:

netstat -ano | findstr :1374

You'll almost certainly see nothing. And that's fine. The port exists in case you ever need to control a machine that grows crystals one atom at a time.

Why Unassigned and Obscure Ports Matter

The port registry contains 65,535 possible ports. Many are unassigned. Many more are registered to services so specialized that most people will never encounter them.

Port 1374 is a reminder that the Internet's infrastructure accommodates everything from massive web services handling billions of requests to control protocols for laboratory equipment in a single building. Every port is a door. Some doors open to the world. Others open to a single room where someone is growing the future of quantum computing, one atomic layer at a time.