How does Wayback Machine work

[BresciaBike]

I think that's its name. The doodah on archive.org that archives the internet. Does it only archive pages people save on it or does it trawl the internet and save pages of its own (programmed 😛) volition?

I think it's a mixture of both but I don't know that and I have wanted to know for ages.

I think it's the latter.