IBM PC Architecture : Memory Addressing

"Standard" addresses (i.e. not "extended") are composed of "segment" and "offset" components. Segment addresses are "paragraph" addresses; offset addresses are byte distances from some paragraph boundary. As implied by the preceding, memory is divided into paragraphs; each paragraph is composed of 16 (10 hex.) bytes.

16-bit Addressing - Precursor to Intel 8086

Prior to the Intel 8086 processor (and the IBM PC, which ensured its popularity), Intel produced a microprocessor called the 8080 which formed the basis for a common generic microcomputer Operating System, CP/M. This processor had a 16-bit address bus and thus supported a maximum of 64K (bytes) of memory.

The 8080's 16-bit address was a "real" address; that is, no conversion was required to transform the 16-bit address value into a "real" or physical memory byte-cell address.

Addressing 1 Megabyte - IBM PC and the 8086

Beyond 1 Megabyte - IBM AT and the 80x86+ family