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.
... and widely disseminated (see DeCSS). See Professor Edward Felton's freedom-to-tinker Web site (www.freedom-to-tinker.com) for some observations on the DCMA, it ...