Download CALDB 3
CALDB 3.3.0 or higher is required for the proper operation of CIAO 3.4. Likewise, do not update to CALDB 3.5.0 unless you are using CIAO 3.4.
The CALDB is a fully functional, fully indexed, updated version of the same CALDB that is used in Chandra standard data processing (SDP); it includes all the calibration files required by CIAO. As explained in the README, the CALDB must be set up in a directory that is accessible from where CIAO will be used.
For more information on the CALDB, including installation instructions, visit the CALDB website.