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The computer that guided man to the moon half a century ago was bulkier and far less powerful than the smartphone you’re sending snaps on today. But the Apollo Guidance Computer was a groundbreaking engineering feat, experts said.

Weighing in at 70 pounds, far smaller than computers of the time that took up whole floors of buildings, the computer marked not just a technological shift, but a cultural shift, experts said.

“At some level, Apollo was the harbinger of computers in everything out in the world,” said MIT engineer and historian David Mindell, who wrote the book Digital Apollo, ” which was published in 2008. “Apollo was the moment people stopped bragging about how big their computers were and started bragging about how small their computers were.”

Most smartphones today have about 4 gigabytes of RAM. That is approximately 1 million times more memory than the Apollo Guidance Computer, Graham Kendall, a computer science professor at the University of Nottingham, wrote in The Conversation.

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The latest iPhone is estimated to have 100,000 times the processing speed of the Apollo computer, Kendall also noted.

But Matthew Hersch, a technology historian at Harvard, said the AGC should be given its due.

The computer “was 30 years ahead of its time,” with excellent software design and a very stable multitasking operating system, he said. Today’s smartphones are not nearly as reliable as the “crash-proof” AGC.

“They’re extremely powerful, unreliable technologies,” Hersch said of smartphones. “A computer operating system on your phone — if it freezes, you can push a button to restart and it’s a minor inconvenience. When you’re on powered descent to the lunar surface, failure is not something you have the luxury of.”

“Your digital watch could never land on the moon because the computer that was on the Apollo was designed to work in an incredibly extreme environment,” Hersch added.

Mindell said a modern smartphone “has many more processing cycles and much greater memory than the Apollo computer, but probably isn’t as powerful if you consider that the Apollo computer never failed in flight and landed 12 people on the moon.” He noted that the computer controlled rocket engines and thrusters to orient the spacecraft, among other mission-critical functions.

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The Apollo computer “was very radical for that day,” said Paul Ceruzzi, a computing historian at the National Air and Space Museum.

He noted that it may be time for rocket technology to catch up. “Computers have got millions and millions of times better. But the rocket efficiency has not improved a whole lot from the Saturn V,” Ceruzzi said, referring to the massive rocket that launched the Apollo on its voyage into space.


Sarah Wu can be reached at sarah.wu@globe.com