How do real time updates work?

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Stack Overflow is using Web Sockets for real time updates. If you take a look in the source code (2012 source code), you would see:

StackExchange.ready(function () {
    StackExchange.realtime.init('ws://sockets.ny.stackexchange.com');
    StackExchange.realtime.subscribeToInboxNotifications();
    StackExchange.realtime.subscribeToReputationNotifications('1');
});

But note that some Opera versions do not support WebSocket. (not until Opera 10.70)

However Facebook does not seem to be using Web Sockets, and I think they are just using simple XHR with a technique called long polling, which the server holds on to the connection until there is new information, and then respond to the request. If you open up the developer tools you can see that there is always one request which has a status of pending.

It is indeed, sending a request every ~60 seconds.

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