Root Name Servers?

[Dave Walton]

Could someone explain just what the root name servers do?

I understand that my DNS Servers translate a Domain Name to an IP Address.
Do the Root Servers just cache this information? Or do they provide another
role? How does a resolution request get routed to the correct Name
Server(s)?

Why does it take up to a week for a change in registered name servers to
take effect?

Thanks

-Dave Walton