The Oldest Computer Still in Use

We live in a world where new tech gets old fast. Last year’s smartphone? Obsolete. A decade-old laptop? Practically ancient. So, what would you say if we told you that the world’s oldest still-operational computer is over 70 years old—and still clicking away? It’s not flashy, and it won’t run Fortnite, but it’s a living, humming piece of history that continues to do the job it was built for.

Meet the Harwell Dekatron, also known as the WITCH (Wolverhampton Instrument for Teaching Computing from Harwell). It’s more than just a machine; it’s a testament to resilience, careful engineering, and the beauty of analog computing. Let’s explore how this behemoth of blinking lights and relays is still computing in a digital world.

How It Was Discovered

The Harwell Dekatron was first commissioned in the early 1950s at the Atomic Energy Research Establishment in Harwell, England. It was built to automate tedious mathematical calculations previously done by hand. At the time, this machine was a marvel, freeing scientists from grueling hours of number crunching.

Surprisingly, the Dekatron wasn’t based on vacuum tubes or silicon chips but on gas-filled counting tubes (called dekatron tubes), relays, and paper tape readers. These components made it incredibly slow by today’s standards, but also extremely reliable. Unlike early transistor-based machines, the Dekatron was designed to be fail-safe and durable, even at the cost of speed.

Behind the Scenes

After serving its purpose at Harwell, the machine was moved to Wolverhampton and Staffordshire Technical College in 1957. There, it earned its WITCH nickname and educated a generation of British computer science students. It remained in active use for educational purposes until 1973—outlasting many of its faster successors.

Then, the machine went quiet. It was disassembled and stored in pieces, nearly forgotten in a dusty warehouse. Decades later, in the early 2000s, a group of dedicated volunteers from The National Museum of Computing began the painstaking process of restoring the WITCH. Piece by piece, they tracked down original parts, recreated lost components, and reassembled the machine according to its mid-century specifications.

In 2012, after nearly a decade of work, the Harwell Dekatron was switched on once again—and it worked. It is now on display, and still running, at The National Museum of Computing in Bletchley Park, UK.

What Most People Don’t Know

• The WITCH uses dekatron tubes that glow as they count—an analog light show of logic in action.
• Each relay click corresponds to a visible step in a calculation, making the machine’s operations fully transparent.
• It still runs programs in machine code, input via punch tape—no GUI, no mouse, just raw computing.
• The WITCH can visually display errors and processing stages, helping users learn basic troubleshooting principles.
• Its modular and repairable design contrasts sharply with modern sealed, disposable electronics.
• WITCH’s rhythmic clicking has been likened to mechanical music—a surprisingly meditative soundscape.
• Still used for education and demonstration, it bridges generations and fosters hands-on engagement with computer history.

What’s more, the WITCH isn’t just a museum piece—it still runs programs written in decades-old machine code. Visitors can load punch tape, input numbers, and watch the machine calculate. It’s not just working; it’s teaching, inspiring, and bridging generations of tech lovers.

Why It’s Still Relevant Today

At a glance, the WITCH may seem like a charming relic—but its continued operation is deeply symbolic. In a time when planned obsolescence is baked into many devices, here is a machine that defies the trend by still performing its original tasks, 70 years on. It underscores the importance of durability and repairability in design—something increasingly rare in the age of disposable tech.

More than that, it reminds us of the physicality of early computing. Today, our devices are sleek, silent, and opaque. But the WITCH brings back the wonder of understanding what’s happening under the hood. You don’t need a debugger to see how it works. Each flickering tube and clacking relay tells a story of computation unfolding, one step at a time.

From Students to Tech Enthusiasts

Part of the WITCH’s charm is its educational impact. During its time at Wolverhampton, it wasn’t just a showpiece—it was a hands-on teaching tool. Students would write their own code in machine language, learn about loops and logic gates, and physically feed data into the computer via punch tape. It gave them a literal sense of programming—something that’s hard to replicate with modern GUIs and high-level languages.

Today, the WITCH still sparks inspiration. Programmers, engineers, and curious visitors travel to Bletchley Park not just to marvel at the past, but to understand the building blocks of modern computation. It’s a tactile history lesson—a bridge between generations of technology lovers.

Its longevity also poses a philosophical question: What should we preserve from our technological past? As AI and quantum computing push boundaries, machines like the Harwell Dekatron ground us in how far we’ve come—and how much effort it took to get here. Every click of a relay is a reminder that today’s miracles once required mountains of hardware and human ingenuity.

There’s beauty in that slowness. In an era of instant everything, the WITCH encourages patience, appreciation, and respect for the analog artistry that paved the way.

Bonus Fact

The Harwell Dekatron holds the Guinness World Record for the oldest original working digital computer. It beats even iconic machines like the ENIAC or Colossus—not because it was built first, but because it’s still fully functional in its original form. Other machines have been rebuilt or replicated, but the WITCH is the real deal, running on many of its original parts.

Takeaway

In a world obsessed with innovation, the Harwell Dekatron is a monument to longevity. It’s proof that great design and careful restoration can keep even the most unlikely machines running for generations. The WITCH may not win any speed tests, but its glow, its click, and its continued operation remind us that history isn’t just in books—it’s in blinking lights and humming relays, still computing after all these years.

Next time you reboot your computer, consider the Harwell Dekatron. It may be slow, but it’s still thinking—one relay at a time.