When you load your heavy PST file in the software to view old PST files, the PST data get loaded in the C folder because it is the installation drive of your PST Attachment Viewer software to view Outlook PST files with attachments. In case you do not have enough space in your C drive, then the PST Viewer software to view PST emails may crash. So for optimized viewing, we have provided the option to change the loaded data path of the PST file.