Data files are huge, and must be compressed to be readily transferred. It keeps file sizes and bandwidth down. There are many ways to compress the image. One of the oldest utilities on the PCs wss called PKZIP, and is a standard (Windows bought it). Files which are zipped have .zip as an extension. The main software on Macs is called STUFFIT, and these files have .sit endings. There are also .rar and .arc and other endings meaning that the file has been compressed, and needs to be extracted before being used. You can download a PC version of Stuffit free from Alladin Software which will open all these file types. Carolly