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.
... Ross J Anderson on his Web site at www.cl.cam.ac.uk/~rja14/tcpa-faq.html/ for a clear discussion of two prominent proposals.
Examples of existing "digital ...