Files with .PST extension represent Outlook Personal Storage Files (also called Personal Storage Table) that store variety of user information. User information is stored in folders of different types that include emails, calendar items, notes, contacts, and several other file formats. PST files are used for archiving emailing data offline that can be later loaded and viewed in various applications.
A GIF or Graphical Interchange Format is a type of highly compressed image. Owned by Unisys, GIF uses the LZW compression algorithm that does not degrade the image quality. For each image GIF typically allow up to 8 bits per pixel and up to 256 colors are allowed across the image. In contrast to a JPEG image, which can display up to 16 million colors and fairly touches the limits of the human eye.
You can also convert PST into many other file formats. Please see the complete list below.