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IN 05h would put the address 0505h on the 16-bit address bus).
The registers had the same width as the address bus.
The Intel 8086, the predecessor to the 286, was originally designed with a 20-bit address bus for its memory.
The external interface also consisted of a 34-bit address bus.
But the part also has a 64-bit data bus and 36-bit address bus.
It has a 16-bit address bus, so we know that 16 bits gives us access to 64K of addressing space.
The original 68000 had a 24-bit address bus and a 16-bit data bus.
The chip has an 8-bit data bus, controlled by two address buses.
The MC68020, introduced in 1985 added full 32-bit data and address buses.
Data and instructions were each addressed by separate 16-bit address bus.
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