DBA_EXTENTS

Extents comprising all segments in the database

Columns
   ___________________________
 
   OWNER
      Owner of the segment associated with the extent
   SEGMENT_NAME
      Name of the segment associated with the extent
   PARTITION_NAME
      Partition/Subpartition Name,if any,of the segment
   SEGMENT_TYPE
      Type of the segment
   TABLESPACE_NAME
      Name of the tablespace containing the extent
   EXTENT_ID
      Extent number in the segment
   FILE_ID
      Name of the file containing the extent
   BLOCK_ID
      Starting block number of the extent
   BYTES
      Size of the extent in bytes
   BLOCKS
      Size of the extent in ORACLE blocks
   RELATIVE_FNO
      Relative number of the file containing the segment header

Related:

Simon Sheppard
SS64.com