Quicktime is a multimedia framework developed by Apple Inc., capable of handling various formats of digital video, media clips, sound, text, animation, music, and several types of interactive panoramic images. courtesy of Wikipedia
On February 11, 1998 the ISO approved the QuickTime file format as the basis of the MPEG-4 Part 14 (.mp4) container standard. By 2000, it became an industry standard, first appearing in QuickTime 6 in 2002. Accordingly, the MPEG-4 container is designed to capture, edit, archive, and distribute media, unlike the simple file-as-stream approach of MPEG-1 and MPEG-2.
Because both the MOV and MP4 containers can utilize the same MPEG-4 codecs, they are mostly interchangeable in a QuickTime-only environment. However, MP4, being an international standard, has more support. This is especially true on hardware devices, such as the Sony PSP and various DVD players; on the software side, most DirectShow / Video for Windows codec packs include an MP4 parser, but not one for MOV.
Download a QuickTime movie (MOV) and save it on your computer
However if you already have QuickTime (or iTunes, which bundles QuickTime) installed on your PC, then the easiest solution is to use