A central shaft driven by an outside waterwheel and connected to each machine by overhead belts was the customary power source for all the machines in a factory

Here's a close-up of one of the Mark I's four paper tape readers. A paper tape was an improvement over a box of punched cards as anyone who has ever dropped -- and thus shuffled -- his " stack" knows.

One of the four paper tape readers on the Harvard Mark I (you can observe the punched paper roll emerging from the bottom)

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One of the primary programmers for the Mark I was a woman, Grace Hopper. Hopper found the first computer " bug": a dead moth that had gotten into the Mark I and whose wings were blocking the reading of the holes in the paper tape. The word " bug" had been used to describe a defect since at least 1889 but Hopper is credited with coining the word " debugging" to describe the work to eliminate program faults.

The first computer bug [photo © 2002 IEEE]

In 1953 Grace Hopper invented the first high-level language, " Flow-matic". This language eventually became COBOL which was the language most affected by the infamous Y2K problem. A high-level language is designed to be more understandable by humans than is the binary language understood by the computing machinery. A high-level language is worthless without a program -- known as a compiler -- to translate it into the binary language of the computer and hence Grace Hopper also constructed the world's first compiler. Grace remained active as a Rear Admiral in the Navy Reserves until she was 79 (another record).

The Mark I operated on numbers that were 23 digits wide. It could add or subtract two of these numbers in three-tenths of a second, multiply them in four seconds, and divide them in ten seconds. Forty-five years later computers could perform an addition in a billionth of a second! Even though the Mark I had three quarters of a million components, it could only store 72 numbers! Today, home computers can store 30 million numbers in RAM and another 10 billion numbers on their hard disk. Today, a number can be pulled from RAM after a delay of only a few billionths of a second, and from a hard disk after a delay of only a few thousandths of a second. This kind of speed is obviously impossible for a machine which must move a rotating shaft and that is why electronic computers killed off their mechanical predecessors.

On a humorous note, the principal designer of the Mark I, Howard Aiken of Harvard, estimated in 1947 that six electronic digital computers would be sufficient to satisfy the computing needs of the entire United States. IBM had commissioned this study to determine whether it should bother developing this new invention into one of its standard products (up until then computers were one-of-a-kind items built by special arrangement). Aiken's prediction wasn't actually so bad as there were very few institutions (principally, the government and military) that could afford the cost of what was called a computer in 1947. He just didn't foresee the micro-electronics revolution which would allow something like an IBM Stretch computer of 1959:

(that's just the operator's console, here's the rest of its 33 foot length:)

to be bested by a home computer of 1976 such as this Apple I which sold for only $600: