Personal Storage Table
In computing, a Personal Storage Table (.pst) is an open proprietary file format used to store copies of messages, calendar events, and other items within Microsoft software such as Microsoft Exchange Client, Windows Messaging, and Microsoft Outlook. The open format is controlled by Microsoft who provide free specifications and free irrevocable technology licensing. The file format may also be known as a Personal Folders (File) or Post Office File. When functioning in its capacity as a cache for Outlook's Cached Exchange Mode feature, it may be called an Off-line Storage Table (.ost) or an Off-line Folders (File). Overview In Microsoft Exchange Server, the messages, the calendar, and other data items are delivered to and stored on the server. Microsoft Outlook stores these items in a personal-storage-table (.pst) or off-line-storage-table (.ost) files that are located on the local computer. Most commonly, the .pst files are used to store archived items and the .ost files to maintain off-line availability of the items. This is an essential feature of Microsoft Outlook. The size of these files no longer counts against the size of the mailbox used; by moving files from a server mailbox to .pst files, users can free storage space on their