Objectid, FID, and OID Fields

ArcGIS Desktop requires that both the independent table and Attribute Table have an objectid field, which contains a unique, long integer value to specify each record. This ID is managed by ESRI software and cannot be changed manually.

In shapefiles and Geodatabase feature classes, the objectid processing method is different from that in an independent table.
--- In a shapefile, The 'fid' field contains objectid and the value starts from scratch.
--- In a separate table in the Geodatabase feature class or Geodatabase, The 'objectid' field contains objectid, and the value starts from 1.
--- In an independent DBASE table, the 'id' field contains objectid, and the value starts from scratch.

When you use ArcGIS Desktop to edit data, different objectid fields have different functions:
--- If a record in a shapefile is deleted, the FID will be re-numbered, so that the value will gradually increase from 0. There is no interval between numbers.
--- If a record in a Geodatabase feature class or a Geodatabase table is deleted, objectid will not be re-numbered and the interval in the list will be saved.
--- If a record in a DBASE table is deleted, the oId will be numbered from 0. There is no interval between numbers.

Data conversion causes objectid to be overwritten.
--- When a Geodatabase feature class is exported or converted to the shapefile format, or when a Geodatabase table is exported to the DBASE format, records in the output shapefile or table will be numbered sequentially from 0.
--- When a Geodatabase feature class is exported or converted to a new Geodatabase feature class, or when a Geodatabase table is exported or converted to a new Geodatabase table, records in the output feature class or table will be re-numbered from 1.

Note these features when selecting fields for join or relate tables. If a shapefile needs to use FID and objectid to join a feature class, because the feature class does not have a record that is objectid = 0, therefore, the FID = 0 record of shapefile will not match any record in feature class.

 

From: http://www.sharpgis.com/forum-viewthread-tid-4605-page-1.html