BID (Block ID)


Every block allocated in the PST file is identified using the BID structure. This structure varies in size according the format of the file. In the case of ANSI files, the structure is a 32-bit unsigned value, while in Unicode files it is a 64-bit unsigned long. In addition, there are two types of BIDs:

  1. Page BIDs use all of the bits of the structure and are incremented by 1.

  2. Data Block BIDs reserve the two least significant bits for internal use; as a result these increment by 4 each time a new one is assigned. Third-party implementations MUST ignore these bits and assign them a value of 0.