This article was previously published under Q171582
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This article discusses the purpose and capacity of each of the followingstorage facilities used by Microsoft Outlook 97 when running as a client toa Microsoft Exchange Server:
Personal Folders (PST) files located on the user's computer.
Offline Store (OST) files located on the user's computer.
Mailbox Folders located on the Microsoft Exchange Server.
Public Folders (PF) located on the Microsoft Exchange Server.
Personal Folders Files Located on Your Computer
One or more .pst files can reside on each user's computer. A .pst can be defined as your primary store or as a secondary store. A primary store means that mail delivered to the Inbox in that file and all of your other default Outlook folders, such as Calendar, Contacts, Deleted Items, Journal, Notes, Sent Items, and Tasks reside there. A .pst file can also be defined as a secondary store, which means you can move items to that file, either manually or with Inbox Rules, from your primary store.
Each .pst file can contain a maximum of 65,535 top level items, and a maximum of 65,535 items in each folder. An item is either a folder, message, task, etc. Upon reaching 16,384 items, you are upgraded to the a large tables format, which increases the limit from 16,384 to 65,535. The total file size of a .pst cannot exceed 2 Gigabytes (GB).
Offline Store (OST) Files Located on the User's Computer
Only one OST file can reside on each user's computer. The OST is alwaysdefined as your primary store, meaning that your mail is delivered to theInbox in that file and all of your other default Outlook folders, such asCalendar, Contacts, Deleted Items, Journal, Notes, Sent Items, and Tasksreside there. The OST differs from the PST in that items residing in it canalso reside in the user's Mailbox on the Server. You can synchronize theOST and Mailbox folders so that they always contain the same information.This allows you to work offline when the server is unavailable; then, whenreconnected to the server, changes made offline upload to the server and mail received while offline downloads to the OST.
The OST file can contain as many folders as you desire and each folder cancontain a maximum of 16,384 (16 kilobytes) records. The total file size ofan OST cannot exceed 2 GB.
Mailbox Folders Located on the Microsoft Exchange Server
A Mailbox Folder for each user is stored on the server in the same databasestore. The server has a capacity of 16 GB for one store, which translatesto millions of records. However, the server administrator may limit thesize of each user's Mailbox Folder.
Public Folders (PF) Located on the Microsoft Exchange Server
Public Folders reside on the server in the same database store. Theycontain information shared by many users. Depending upon accesspermissions, individual users can read, update, or add to the PF. Theserver has a capacity of 16 GB for one store, which translates to millionsof records.
For more information about this subject, please see the following articlesin the Microsoft Knowledge Base:
161725 OL97: What Are Offline Folders and How Do You Use Them?