Tuesday, 13 March 2012

Personal Storage Table

In computing, a Personal Storage Table (.pst) is an accessible proprietary book architecture acclimated to abundance copies of messages, agenda events, and added items aural Microsoftcomputer application such as Microsoft Exchange Client, Windows Messaging, and Microsoft Outlook. The accessible architecture is controlled by Microsoft who accommodate chargeless blueprint and chargeless certain technology licensing.

The book architecture may additionally be accepted as a Personal Folder Book or a Personal Address Book (.pab). When activity in its accommodation as a accumulation for Outlook's Cached Exchange Mode feature, it may be alleged an Off-line Storage Table (.ost) or an Off-line Folder File.


In Microsoft Exchange Server, the messages, the calendar, and added abstracts items are delivered to and stored on the server. Microsoft Outlook food these items in a personal-storage-table (.pst) or off-line-storage-table (.ost) files that are amid on the bounded computer. Most commonly, the .pst files are acclimated to abundance archived items and the .ost files to advance off-line availability of the items.

The admeasurement of these files no best counts adjoin the admeasurement of the mailbox used; by affective files from a server mailbox to .pst files, users can chargeless accumulator amplitude on their mailservers.1 To use the .pst files from addition area the user needs to be able to admission the files anon over a arrangement from his mail client. While it is accessible to accessible and use a .pst book from over a network, this is unsupported, and Microsoft advises adjoin it, as .pst files are decumbent to bribery back acclimated in this manner.2

Both the .pst and .ost files use a fixed-block-based allocation scheme; the book is continued by a anchored bulk of bytes, and the book internally maintains advice about the allocated and non-allocated blocks. So, back abstracts files like email letters are added to a .pst file, its book admeasurement is automatically adapted by the mail applicant (if necessary). Back mail is deleted from a .pst file, the admeasurement of the .pst book will break the same, appearance the amplitude as unallocated so that it will authority approaching abstracts items. Recently removed abstracts items can absolutely be recovered from .pst and .ost files.

To abate the admeasurement of .pst files, the user needs to bunched them.3

Data access

Password aegis can be acclimated to assure the agreeable of the .pst files.4 However, Microsoft admits that the countersign adds actual little protection, due to the actuality of frequently accessible accoutrement which can abolish or artlessly bypass the countersign protection.5 The countersign to admission the table is stored after the aboriginal and aftermost XOR CRC-32 accumulation representation of itself in the .pst file. Outlook checks to accomplish abiding that it matches the user-specified countersign and refuses to accomplish if there is no match. The abstracts is clear by the libpst activity code.

Microsoft (MS) offers three ethics for the encryption setting: none, compressible, and high.

None the .pst abstracts is stored as apparent text.

Compressible the .pst abstracts is encrypted with a byte-substitution blank with a anchored barter table.

Aerial (sometimes alleged "better") encryption is agnate to a WWII German Enigma blank with three anchored rotors.

Note that neither of the two encryption modes uses the user-specified countersign as any allotment of the key for the encryption.


The .pst book architecture is accurate by several Microsoft applicant applications, including Microsoft Exchange Client, Windows Messaging, and Microsoft Outlook. The .pst book architecture is an accessible architecture for which Microsoft provides chargeless blueprint and certain chargeless apparent licensing through the Accessible Specification Promise 6

The libpst activity includes accoutrement to catechumen .pst files into accessible formats such as mbox and LDAP Data Interchange Format. libpst is accountant beneath the GPL and is now included in Fedora 10. MVCOM is a commercially accountant COM Component that provides admission to .pst files after MAPI.

There are accoutrement to catechumen .pst to added formats or to upload to added online e-mails like Gmail, for example.7

Formats and size

The book is structured as a B-tree with 512 byte nodes and leafs.8

Outlook 2002 and beforehand use ANSI (extended ASCII with a codepage) encoding for their .pst and .ost files. This architecture has a best admeasurement of 2 GB (231 bytes) and does not abutment unicode. A book beyond this admeasurement is acceptable to accord absurdity messages, such as ".pst has accomplished best admeasurement limit," and could become corrupted. Although superseded, this architecture continues to be accurate by Microsoft Outlook 97 and after (98, 2000, 2002 (XP), 2003, 2007), by Internet Message Access Protocol Adaptation 4rev1 (IMAP4) accounts and by HTTP accounts.9

From Outlook 2003 and onward, the accepted architecture for .pst and .ost files is Unicode (UTF-16 little-endian). The use of 64-bit pointers instead of the 32-bit pointers of the beforehand adaptation accustomed to affected the 2 GB limit. Now, there is a user-definable maximum-file admeasurement up to 20 GB. This architecture is accurate by Microsoft Outlook 2003 and after (2007) 910 A book that is created in the personal-folders architecture in Outlook 2003 or in Microsoft Office Outlook 2007 is not accordant with beforehand versions of Microsoft Outlook and cannot be opened by application those earlier versions.1 If this absolute is accomplished or sometimes exceeded, retrieval of the .pst book can be difficult if not impossible.

As with any file, .pst files can become corrupted. Prior to Outlook 2003, the absence .pst book architecture was ANSI and had a best admeasurement of 2 GB. If the .pst book were accustomed to abound over 2 GB, the book would become unusable. Microsoft provides PST2GB a apparatus that can be acclimated to abbreviate a .pst book that has developed over 2 GB. Microsoft additionally provides scanpst.exe, that can be acclimated to adjustment added .pst file-corruption issues. In Outlook 2003 and 2007, .pst files are created in the Unicode architecture and accept a absence best admeasurement of 20 GB. Outlook 2010's absence best admeasurement has added to 50GB.11

Entourage and Outlook for Mac

Microsoft Entourage is Microsoft's email and claimed advice affairs for Mac OS X. While apparently agnate to Outlook, it is an absolutely altered application, and uses a different database architecture which cannot be alien or exported, admitting user abstracts can be alien and exported to and from addition different architecture alleged .rge (a array consisting of abounding alone files additional metadata). Entourage 2008, the accepted adaptation as of May 2010, has no abutment for .pst files, admitting there exists Microsoft's .pst acceptation apparatus for Entourage 2004; however, the apparatus could alone acceptation .pst files from Outlook for Mac 2001, and not any Windows versions. Entourage is actuality replaced by Outlook for Office 2011 for Intel Macs, which will be able to acceptation Outlook .pst files from Windows;12 however, abstracts will be stored as abounding alone files, rather than in a distinct database such as .pst or the Entourage database.

Outlook for Mac 2001, which runs beneath Mac OS 9 or the Mac OS X Classic Environment, connects alone to Exchange servers, and to this day is afterpiece to its Windows analogue than Entourage is. It works anon with 'Outlook 97-2002' .pst files, and can advisedly altering those files with Outlook for Windows, as contempo versions are still accordant with the earlier .pst format.