Consider the notification system in Google calendar. It sends you a push/email notification user specified time (like 10 minutes/10 hours etc). How is this implemented on the server side? Assuming Google calendar is on a PHP/Apache platform, *is there a script which runs continuously and checks the current time against the time in database and then push notifications when the times match?*
**Basic question - how does the server know when to push the notifications?**

Is it easier to do this on Apache/PHP or Node.js?