In the timeline that I have provided, shows when iMovie was born and the years when Apple updated their versions.
On October 5, 1990 the first iMovie was released for Mac OS 8.6 and OS 9 systems. At first it was bundled wth iMac DV, and then later available as a free download online.
On July 19, 2000 another version was avalible for the Mac systems OS9 and OS X called "iMovie 2." At this time, it was bundled with FireWire-enabled Macs but was also avalible seperatly for purchasing.
iMovie HD 5 was released on January 6, 2004 for the most recent system Mac OS X with free downloads for owners of iLife '05. More versions of iMove HD came out in the next couple of years for the newer systems also.
On June 24, 2010 iMovie became available (to purchase) for iPhones and iPod touch via App Store. Then later available for the iPad on March 10, 2012.