The A20 handler is IBM PCmemory manager software[?] providing HMA[?]. XMMs[?] usually provide this functionality. Named after the 21st address line (A20), controlling the access to HMA.
... Jerónimo de Yuste[?], Spain September 21, 1558) was Holy Roman Emperor (as Charles V) from 1519-1558; he was also King of Spain from 1516-1556 -- officially as Charles I ...