What are the differences of MARC21 and UNIMARC?

Nowadays libraries collect and gather different kinds of material in all formats (books, periodicals, newspapers, tapes, pamphlet, CD, electronic materials,. ..), subjects and languages that will be suitable for their users. So they should have proper catalgue and desirable bibliographic services to help the users find their required information and satisfy their needs. One of the best solutions for this problem is using MARC format for libraries bibliographic network. UNIMARC and MARC21 are the most populare and known MARC formats in the world. So the aim of this research is to compare these two formats (UNIMARC and MARC21) and reveal the weaknesses and strengths of them. The results of this compatision could help libraries for choosing the best basis formats for theirs bibliographic network. In this research, the comparison of these two MARCs is done in different features as history and performance, content and structure, by the last available version of UNIMARC (2012) and MARC 21 (2015). Data analysis showed in all aspects, MARC 21 has more capability than UNIMARC.