Ask Hackaday: Understanding The X86 Memory Addressing System

A quick look at the pinouts of an Intel 8086 & 8088 processor reveals a 20 bit address bus. There was high demand for the ability to address 1 meg (2^20) of address space, and Intel delivered. However, a curious individual would wonder how they can achieve such a feat with only 16 bit registers. Intel solved this riddle by combining two registers so they could make it compatible with code written for the 8008, 8080 & 8085. The process they use can be a bit confusing when trying to figure out where to locate your code in the ROM. In this article, we are going to go over the basics of how the Physical Address is calculated and how to locate your code correctly in ROM.

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