How do short URLs services work?

Question

How do services like TinyURL or Metamark work?
Do they simply associate the tiny URL key with a [virtual?] web page which merely provide an \"HTTP redirect\" to the orig

Answer 1

As an extension to @A Salcedo answer:

Some url shortening services (Tinyarro.ws) go to extreme by using Unicode (UTF-8) to encode characters in shortened url - which allows higher amount of websites before having to add additional symbol. Since most of UTF-8 is accepted for use ((IRI) RFC 3987 handled by most browsers) that bumps from 62 sites per symbol to ~1,112,064.

To put in perspective one can encode 1.2366863e+12 sites with 2 symbols (1,112,064*1,112,064) - in November 2009, shortened links on bit.ly were accessed 2.1 billion times (Around that time, bit.ly and TinyURL were the most widely used URL-shortening services.) which is ~600 times less than you can fit in just 2 symbols, so for full duration of existence of all url shortening services it should last another 20 years minimum till adding third symbol.