About 'hosts' file uses.
Dunno if our Nocturnal Predator groks "hosts" - if so, just ignore.
Whenever you go to a URL which is a name (and not unique address xxx.xxx.xxx.xxx) there occurs a "DNS lookup" to convert to the actual server address. In principle, such a change percolates down to your nearest switch/whatever "pretty quickly" and you never notice a few millisec. wasted lookup time for every URL. As Greg notes - not necessarily so quickly to percolate down, today.
IF you *have a "hosts" file in the locations mentioned above, AND type in the above entries:
Instead of using web DNS lookup, your Stack will first look in hosts. Problem solved. Note that another use for this file, is to obtain any number of collections of AD-server [doubleclick.net et al] locations and assign each one an address of, "127.0.0.1" == which is your own "localhost" address and means:
That ad will go directly to pugatory (or your fav other imaginary place).
*sometimes "hosts" is renamed to 'hostx'(or other) so it WON'T be queried. While hosts will speed you on your way, it can also miss the fact that a URL has changed address, and produce an error / or no action - for a working site. SO you have to remember you *are* using a hosts file! when a popular site "goes missing".
You can then use "DNS lookup" to find out the new address and correct your hosts file. It's ANNOYING when one forgets hosts is in use...
HTH,
Ashton