Everyone knows what a computer is, right? It's electronic, high-tech and digital. It's only existed for the last 50 or 60 years. It has defined the word "modern" in “modern world.” And it’s given hackers a useful role to play in big-budget action movies.

But computers actually date back thousands of years. Here are a handful of the most interesting predecessors to the modern PC, and what folks in olden times used them for.

1. The Antikythera mechanism

A mysterious object recovered from a shipwreck, this first-century device has stunned researchers. Its fine workmanship and impeccable mechanism wouldn't be matched for more than 1000 years.

When recovered in 1901, its discoverers had no idea of its origin or purpose. Over the decades, scientists have theorized that it was a portable device that allowed its user to input the date and learn the position of the Sun, Moon, and other astronomical phenomena.

In recent years, computed tomography scans have revealed even more intricacies. The mechanism is considered by some to be the earliest surviving computer.

2. The Stepped Reckoner

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Gottfried Leibniz, a German mathematician and all-around genius (he created differential calculus), invented the first four-function calculator in 1673. It used a metal cylinder to represent the digits from 0 to 9, and its basic design was used in mechanical calculators into the 1970s and 1980s. The hand-cranked Curta calculator is a direct descendent.

There was a fairly significant problem with Leibniz’s device, though. His design outstripped the ability of workmen at the time. His calculator didn’t actually work that well when built. And even when fully restored to his original specifications in the late 1800s, the reckoner didn’t carry tens correctly.

3. Difference Engine

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The most famous analogue computers were created—although not fully built—by the English pioneer Charles Babbage.

He first proposed the Difference Engine—a giant, automatic calculator—in 1822. The British government ended its funding for the project some two decades later, after Babbage had spent 17,000 pounds without creating a usable machine. He had created a lot of high-quality industrial tools to make the gears a Difference Engine might use, though.

4. Analytical Engine

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Babbage didn't stop to mourn. He had already moved on the Analytical Engine, the very first general-purpose computer. His design (which spanned thousands of pages) included the main elements found in modern computers—including programs installed via punch cards. Babbage worked until his death in 1871 to realize his creation, but neither her nor his heirs managed to construct one.

5. MONIAC (Monetary National Income Analogue Computer)

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This analog computer, created in 1949, modeled the economic workings of the United Kingdom through a series of water tanks. Water flowed through MONIAC from a reservoir, representing the treasury, perched at the top of the system. Taxation was represented by water pumped from the lower tanks back to the top one.

While this type of computer was displaced by digital devices, MONIAC has lived on in fiction. It appeared in thinly disguised form in fantasy author Terry Pratchett’s 2007 novel, Making Money.