How long does a patent protect a technology?

Ideally, the term of enforcement of a U.S. patent is for 20 years from the earliest non-provisional application filing date. I say ideally because time consumed to prosecute the patent application to allowance "eats into" this 20 year term. So the sooner you get your patent application to allowance, the more of the 20 year term your enforceable patent will entail. While the patent application is pending, there are no enforceable patent rights, although there is something known as "provisional rights (PR)". This means that if your patent application is published (typically 18 months after the earliest filing date) and your patent application is eventually allowed and issues into a patent, AND IF the claims of your published patent application are substantially identical to the claims of your issued patent (which is usually NOT the case), then it may be possible to collect a reasonable royalty from infringers as far back as the publication date of your patent application. With regard to the "original moment of invention", if that is means an inventor reduced his invention to practice before he/she filed the first patent application, under the new America Invents Act, that date is not considered as part of the 20 year term.