What is Difference between Outlook OST and PST File Format?

Microsoft Outlook is one of the widely used email client developed by Microsoft. If you have ever worked in the outlook you must have listened about the Outlook Data File (OST and PST file). Entire data of Outlook including emails, calendars, tasks and notes etc. is stored in these file format.

When Outlook creates OST and PST Files:

1). Microsoft Outlook creates PST file to store the data of IMAP, POP3 and web-based email clients. After the release of Outlook 2013 outlook started creating OST file instead of PST file to store the data of IMAP account.

2). When Outlook is configured with Exchange Server along with Cache Exchange Mode enabled then it stores the data in OST file format.

Detailed Information about OST and PST File format: .OST vs .PST

PST File Format: PST file stands for Personal Storage File which is used to store the emails, contacts, calendars, tasks notes etc. in the local storage of your computer. When we create an account in the outlook, it automatically creates the PST file. We can also add password to PST file if required to prevent the access from unauthorized peoples.

  • The Outlook 2002 and all its previous versions supports ANSI coded PST file which has a size limit of 2GB.
  • The Outlook 2003 and onwards version of Outlook supports Unicode PST file with having size limit of 20GB.
  • The Outlook 2010 has PST file size limit of 50GB.

OST File Format: OST file stands for Offline Storage Table. It is created when cache exchange mode is enabled and Outlook is configured with mailbox of exchange server. If we disable the cache exchange mode then No file will be create on the local machine. Outlook will access the data directly from Exchange Server.

In OST file we can even work in offline mode i.e. when there is no connection with the exchange server. The changes done in the OST file will be reflected back to the exchange server when it is online. OST files can only be used in the computer in which it is created. You cannot open the OST file in any other computer. If due to some reasons your OST file has lost connection from Outlook then you would not be able to open the OST file even in the same Outlook in which it was created. In that case you will need to convert OST to PST to view its content.

In case of corruption in OST file we can use the inbuilt tool ScanOST.exe developed by Microsoft to repair it.

Location of OST and PST File:

To check the location of PST file the simplest and fastest method is given below:

  1. First of all click on file button -> Account Setting
  2. Then click on Data File Tab.
  3. Select the OST or PST file whose location you want to see and Click on Open File Location


In this article we have explained difference in .ost vs .pst file format. Hope you like the information given in this article. If the information is helpful to you in anyway, kindly do comment and let us know in the commend section.

2 thoughts on “What is Difference between Outlook OST and PST File Format?”

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