"Addressing capacity
The 8086, 8088, and 80186 have a 20-bit address bus, but the unusual segmented addressing scheme Intel chose for these processors actually produces effective addresses which can have 21 significant bits. This scheme shifts a 16-bit segment number left four bits (making a 20-bit number with four least-significant zeros) before adding to it a 16-bit address offset; the maximum sum occurs when both the segment and offset are 0xFFFF, yielding 0xFFFF0 + 0xFFFF = 0x10FFEF ... the actual amount of memory addressable by the 80286 and later x86 CPUs in real mode is 1 MB + 64 KB – 16 B = 1,114,096 B."
https://en.wikipedia.org/wiki/Real_mode
El ejemplo del que parte esa pregunta no es de modo real sino de:
https://en.wikipedia.org/wiki/Unreal_mode
The 8086, 8088, and 80186 have a 20-bit address bus, but the unusual segmented addressing scheme Intel chose for these processors actually produces effective addresses which can have 21 significant bits. This scheme shifts a 16-bit segment number left four bits (making a 20-bit number with four least-significant zeros) before adding to it a 16-bit address offset; the maximum sum occurs when both the segment and offset are 0xFFFF, yielding 0xFFFF0 + 0xFFFF = 0x10FFEF ... the actual amount of memory addressable by the 80286 and later x86 CPUs in real mode is 1 MB + 64 KB – 16 B = 1,114,096 B."
https://en.wikipedia.org/wiki/Real_mode
El ejemplo del que parte esa pregunta no es de modo real sino de:
https://en.wikipedia.org/wiki/Unreal_mode