What is the difference between pst and ost?

OST :Offline Storage File

PST :Personal Storage File

both are MS Outlook files. OST files is unreadable but PST file is readable.

OST file is Outlook Off-line Storage Table data that is not readable but PST file is Outlook Personal Table data is readable file.

More helpful link for OST to PST conversion and discussion follow this blog: -

http://geekswithblogs.net/Convert-OST-to-PST