[Koha] On basic differences of MARC, MARC21 and UNIMARC

[zolot]

Hello all, 

"Koha 3.14. Manual (en)" considers "MARC", "MARC21" and "UNIMARC".

What principle differences exist between these formats ? 

My database (more preciesely, isis-catalog, 100 000 records) has been created in accordance with Ukrainian standard "UKRMARC".

Which of the indicated formats must be chosen for preferences ?

What criteria need to be followed for the choice of marc-format ?


Thank you,
Gennady