Found out the Apollo 11 guidance computer had less power than a calculator

I was reading through this NASA history page last night and it hit me - the computer that got men to the moon only had 2 kilobytes of RAM. That's less than what's in my basic TI-84 from high school. Makes you wonder how they pulled it off with such limited hardware. Has anyone else looked into the specs of old space tech and been surprised?

3 comments

3 Comments

amy97426d ago

The guidance computer was basically a stripped down system where every byte had a job. Engineers wrote programs in assembly and literally planned out every single instruction by hand on paper first. I got into this because I was trying to figure out how my old graphing calculator worked and ended up down a rabbit hole about the Apollo computer. Their approach was to keep the software dead simple and test it over and over again until it was bulletproof. If you ever try to run old code on those vintage emulators you'll see how they used things like core rope memory which stored bits as wires woven through magnetic rings. It was less about raw power and more about making every single operation count.

josepha3226d ago

You mentioned core rope memory and how they wove bits through magnetic rings - I've read about that too but I'm still fuzzy on how they actually programmed it. Was each program basically burned in physically, meaning they couldn't change it once the rope was woven? If a bug turned up during testing did they have to unwind and reweave the whole thing? That just sounds like a nightmare compared to today where you can just push an update.

taylor1226d ago

Man, that core rope memory stuff is wild. I got obsessed with this a few years back and even tried writing a tiny assembly program for a simulated Apollo guidance computer in my spare time. It was painful. You had to plan out every single register and memory address by hand, and if your math was off by one byte the whole thing crashed. I can't imagine doing that for an actual moon mission. The fact that they wove the actual program into those magnetic rings, and if you messed up you had to physically rethread the whole rope, is just insane. Makes me feel like a spoiled brat clicking "compile" on my laptop today.