architecture - How are user sessions/data stored on web servers? -

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i'm starting web development in earnest, more static pages, , keep wondering, how data stored per user on server? when 1 user submits form post, , gets looked on page, how can server tell user1's fooform data user2's fooform data? know can keep track of users cookies , http requests, how server keep these data sets available? there tiny virtual machine each user session? or kind of paging system user's content served, , server swaps process out while system thread? i've wondered how site million concurrent visitors manages serve them , keep individual user sessions contained.

i'm familiar os multithreaded architecture , algorithms, idea of doing anywhere 1 million separate "threads" on anywhere 1 n separate machines mind blowing.

do algorithms change scale does?

i'll stop before ask many questions , gets broad, i'd love expertise elucidate me, or point me resource.

thanks reading.


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