CPGZ is a compressed version of a CPIO file. CP refers to CPIO which is the main file, while GZ refers to GZIP, the compression utility.  Files that have the CPGZ extension can typically be found in computers that run Mac OS X or the Unix platform.

CPIO (Copy In Copy Out) files generally works as a file archiving utility.  Its original design was for the Programmer’s Workbench under the UNIX system or platform.  From its original design, the CPIO file has been revised several times with some versions resulting to incompatibilities between different platforms.  With its wide use in the UNIX platform, CPIO files are also supported under the Mac OS X platform.  This explains why many users of the iPad for example encounter files with the CPGZ extension.  Seeing these files simply mean that the archiving utility files in the form of CPIO are being compressed through the GZIP utility.  Opening these files therefore requires unzipping or decompressing the contents.

For the non-tech-savvy person, opening CPGZ files may be quite complicated if he/she is not familiar with file compression utilities like GZIP.  In these cases, one may just double click on a file with CPGZ extension and let the computer open it with the default program.  Most of the time, one’s computer will know which program to use in handling files like CPGZ.  If the file does not open this way, one may need to try other techniques. For both UNIX and Mac OS X platforms, using the ditto utility of the BSD command line may do the trick in extracting the contents of a CPGZ file.  For Apple computer users, they may also use the BOM Archive Helper to view the contents of a CPGZ file.  In cases where Windows users will encounter CPGZ files, using the WinZip utility may easily do the trick.  If without WinZip installed, a good alternative compression utility is 7-ZIP.