ACCDB File Format
Definition - What does ACCDB File Format mean?
The .accdb file format is the default file-saving format for the Microsoft Access 2007 and 2010 database applications. Previous versions of Microsoft Access, like 2000 and 2003, use the .mdb file format by default.
Techopedia explains ACCDB File Format
The .accdb file format is analogous to the .docx and .xlsx formats of Microsoft Word 2007 and Excel 2007, respectively. In fact, the .accdb format is more widely known as “Access 2007” file format. Databases created or saved as .accdb files cannot be opened by versions of Microsoft Access prior to 2007, which includes Access 95, 97, 2000 and 2003. Databases created in the earlier .mdb format can be converted to .accdb databases by simply opening them in Access 2007 or 2010 and saving in the newer file format. Of course, the new Access 2007 and 2010 are also fully backward-compatible with older .mdb files.
The .accdb format supports some new features, such as multivalued fields, data macros, ability to include attachments in the database, integration with Sharepoint and Outlook, and publishing to Access services. However, some older features like replication and user-level security are no longer supported in the new format.
Even though both Access 2007 and 2010 use .accdb by default, there are some newer features available in Access 2010 that are not available in 2007. Examples of these are: updated database sort orders in some languages, Access 2010 encryption compliance, data macros and calculated columns. Most of these are advanced features whose absence in Access 2007 should not be a problem for most users.