Port 526 was assigned to TEMPO, also called "newdate"—a network time synchronization protocol developed for distributed Berkeley UNIX systems in the early 1980s.
What TEMPO Was
In 1984, keeping clocks synchronized across networked computers was a new problem. Different research groups were developing different solutions. TEMPO was one of them—a network time controller designed to keep distributed UNIX systems running on the same clock.1
The problem TEMPO solved is the same one we still face today: computers drift. Every system clock runs at a slightly different speed. Without synchronization, a distributed system falls apart. Timestamps become meaningless. Logs can't be correlated. Coordinated operations fail.
TEMPO was documented in the IEEE Distributed Processing Technical Committee Newsletter in June 1984. It was a serious attempt at network time synchronization, assigned an official port number in the well-known range.
What Happened
TEMPO lost.
Around the same time, David L. Mills at the University of Delaware was developing what would become the Network Time Protocol (NTP). The first version of NTP was released in 1985.1 NTP was more sophisticated, more accurate, and better designed for the growing Internet.
By the 1990s, NTP had become the standard. TEMPO faded into obscurity. Port 526 remained assigned—a reserved space for a protocol that nobody uses anymore.
Why This Port Matters
Port 526 is a fossil. It's evidence of a moment in Internet history when the problem of network time synchronization was still being figured out. Multiple protocols competed. Different approaches were tried. Eventually, one won.
The well-known ports range (0-1023) is full of these fossils—services that were important enough to get official assignments but not successful enough to survive. They're a reminder that the protocols we take for granted today (HTTP, DNS, SSH, NTP) weren't inevitable. They won competitions against alternatives that seemed just as promising at the time.
TEMPO is gone, but the problem it tried to solve is still essential. Every NTP query that synchronizes your computer's clock is solving the same problem TEMPO was designed for. The question doesn't change. Only the answer does.
Current Status
Port 526 is still officially assigned to TEMPO in the IANA registry, but the protocol itself is effectively dead. You won't find modern systems running TEMPO.
Some security databases note that port 526 has occasionally been used by malware to communicate—a common fate for abandoned ports. When a port is assigned but unused, it becomes available real estate for anything that wants to communicate without drawing attention.
Checking What's Listening
If you want to see if anything is listening on port 526 on your system:
Linux/Mac:
Windows:
If something is listening, it's not TEMPO. It's either malware or a modern service that's repurposed an abandoned port.
The Well-Known Ports
Port 526 sits in the well-known ports range (0-1023), which is managed by IANA and reserved for core Internet services. Getting a port assigned in this range meant something in 1984—it meant your protocol was considered important enough to deserve a permanent address.
Many of these assignments didn't age well. The well-known ports range is full of protocols that seemed essential at the time but were replaced by better solutions. TEMPO is one of them.
The Internet doesn't delete its history. It just stops using it and moves on.
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