Liz says:

If I am understanding you question correctly, places like godaddy and yahoo and all of those places. Well the exact physical structure is probably a closely held secret, but basically you are dealing with banks and banks of rack mounted servers, petabytes of storage, . and just a pile of band-width. You can host your own server just as easily as any of the the big guys is you want to. All you need is either a static IP address or a dys-dns service and some kind of web-server. I use apache myself. free, and works just fine.