The datastore.edb file is a database of Microsoft Windows updates. It can grow quite large and affect the performance of a personal computer. It is located in the %windir%/SoftwareDistribution/Datastore directory on the computer's hard drive.
Initially, the datastore.edb file can be used to accomplish two things: ensuring a Windows installation uses Microsoft Update from the start and hiding any updates that need to be excluded from Windows/Microsoft Update. Other .edb files used by Windows include contacts.edb, which stores contact information in Microsoft Live products, and windows.edb, which stores index information used by Windows for search features. EDB is an acronym for Exchange Database.