What is a PST File and What does It Store?
PST is short for Personal Storage Table. Outlook uses the file to store emails, attachments, contacts, calendars, tasks and notes on your computer.
Microsoft states that POP accounts store their data in PST data, while Microsoft 365, Exchange, IMAP and Outlook.com accounts use OST files. Extra PST data serve archives and backups too.
| Detail | PST |
|---|---|
| Extension | .pst |
| Full form | Personal Storage Table |
| Maker | Microsoft |
| File kind | Binary file that holds a tree of folders and items |
| Default folder | Documents\Outlook Files |
| File signature (hex) | 21 42 44 4E |
How Large can a PST File Grow?
Outlook 2002 and earlier use the old ANSI format, which stops at 2 GB. Outlook 2003 and later use the Unicode format, and Microsoft sets the default limit at 50 GB.
Check the format in Outlook. Right click the root folder of the file, select Data File Properties and then Advanced. A format of Outlook Data File (97-2002) means ANSI.
Large files open slowly and break more frequently. Microsoft explains how to shrink a data file with Compact Now, and Microsoft documents the size limit settings for administrators. Our guide to split a large PST shows the safe way to divide one.
How do You Open the File?
Method #1: Open It in Outlook (Free)
Windows cannot open a PST with a double click. Start Outlook, select File, then Open & Export and Open Outlook Data File. Our guide to the must be opened from within Outlook message explains why.
Method #2: Open It Without Outlook (Paid After Demo)
A PST viewer opens the file with no Outlook installed. Use it when you have a file from an old computer and no license. Our PST repair tool guide lists tools that recover damaged files too.
What Causes PST File Errors?
- A file that grew past its size limit.
- A crash or power cut while Outlook had the file open.
- A file saved on a network drive, which Microsoft does not recommend.
- A damaged disk.
Use the Inbox Repair Tool for light damage, and see our Outlook data file errors guide for the message you see. Compare it with the offline format in our OST file guide.
Frequently Asked Questions
What does PST Stand for?
PST stands for Personal Storage Table. Outlook calls it an Outlook Data File too.
Where is the PST in Windows?
Outlook saves PST data in Documents\Outlook Files by default. Open Account Settings and the Data Files tab to see the exact path.
How Big can the File Get?
The Unicode format has a 50 GB default limit, and the old ANSI format stops at 2 GB.
Can You Open It Without Outlook?
Yes, with a PST viewer. Windows has no program that opens it by double click.
Do POP Accounts Use PST?
Yes. Microsoft states that POP accounts store their data in PST data.
Is PST the Same as OST?
No. PST stores local archives and POP mail. OST mirrors a server mailbox, and Outlook can rebuild it.
Can You Repair a Damaged File?
Yes. The Inbox Repair Tool fixes light damage. Repair software handles files it cannot open.
Author's Verdict
A PST stores data that no server copies for you, so backup every PST you rely on.
Open the file from within Outlook, and split it before it nears the size limit.
Key Takeaways
- PST means Personal Storage Table.
- The Unicode format has a 50 GB default limit.
- You must open the file from within Outlook.
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