File packed first using Pak200 (to create a .PACK file), and then compressed using gzip compression (into a .GZ file); used to reduce the file size of a .JAR file for download over the Internet. PACK.GZ files are commonly used by Java Web Start clients to retrieve and unpack JAR files over the Internet for Java applications. NOTE: PACK.GZ files may be decompressed into PACK files using a gzip decompression utility, but they cannot be restored to the original JAR file without using Pack200.