Segment summery views - do they exist?

I wonder if anyone out there has written scripts to create views that contain information about all segments, such as

segment_name
maximum size of a row (in bytes)
average size of a row (in bytes, using VSIZE) number of rows in the segment/table
total number of bytes allocated
total number of bytes used

If a table row consists of one column, say NAME char(20), and there's only one row in the table where name is 'ABCDE', how many bytes in the extent are USED? I would hope only 5 and not 20, but would like this confirmed.

Thank you.

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Chris Little, Programmer/DBA                    Computing & Data Services
                                                University of Scranton
  LITTLEC1_at_JAGUAR.UOFS.EDU                      Scranton, PA 18510