Re: [TUHS] How to do differential/integral on a PDP-7, was: Space Travel

On 19 Oct 2019 16:40 -0400, from krewat(a)kilonet.net (Arthur Krewat): Indeed; like I said, at some point, it becomes just a matter of how quickly you need the answer. It's not really _difficult_ to do any of this if you're willing to wait a while to learn the value of 1/2. It's a little more involved if you want log10(e^pi * pi^e) _fast_. After all, Apollo navigated to, around, and back from, the Moon, using an on-board computer that today would barely run that thermostat that someone mentioned. 2048 15+1-bit word RAM (3840 bytes, plus parity), 36864 15+1-bit word ROM (69120 bytes, again plus parity). It could display three general-purpose five-digit decimal numbers, each with sign, plus three specific-purpose two-digit decimal numbers, and was operated using a 19-key keyboard (0-9, plus, minus, and a few function keys). In fairness, a lot of the heavier calculations were performed by Mission Control on the ground and the results were uplinked either digitally or via voice transmission to the spacecraft, but still... Those programmers didn't exactly have the luxury of, when they realized they were running out of memory, just sending along the rest of the software on tape and telling the user to load it on an as-needed basis. Premature optimization is the root of all evil in 99% of the cases, but in that last 1%, a targeted optimization effort is exactly what you need. -- Michael Kjörling • https://michael.kjorling.se • michael(a)kjorling.se “The most dangerous thought that you can have as a creative person is to think you know what you’re doing.” (Bret Victor)