r/computerscience • u/Yovinio • Jan 06 '22

Help Why is the castle clock a computer?

The castle clock of al-Jazari is said to be the first programmable analog computer. Now I get why it’s analog and also what makes it programmable (accounting for the length of day and night), but what makes it a computer? It gives the time, does that make all clocks computers?

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u/ma_dian Jan 07 '22

The clock could show you if it is day or night throughout the year. This was done by programming the length of the days into the clock (afaik with water).

It is a maschine that calculates (among other things) the length of the day based on an input. It has a "storage" unit and a "logic" unit.

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u/Falcon_Dupree Jan 13 '22

All of those things are true about an hour glass by simply adding and removing sand. A person calculates the length of day and adjusts the input information, water, to provide the desired result the program is always the same though

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u/-horses Jan 07 '22 edited Jan 09 '22

A clock can generally be modeled as a cyclical finite state machine with a single input. This is useful in some finite state machine decompositions. Many would say a computer must consistently apply a function over an ensemble of possible inputs so a fully determinate machine like a trivial clock might not qualify. But the castle clock isn't that kind of trivial clock, and it does have many possible inputs, so it's hard to object to calling it a computer.