Since EU and BIU are independent, whenever the EU starts decoding and executing fetched instructions, the BIU actively fetches additional instruction bytes to keep the queue filled. Externally, the 20‑bit address bus enables the processor to access up to 1 megabyte of physical memory. The BIU calculates physical addresses by shifting a segment register left by 4 bits and adding the offset.
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Only the BIU differs between the 8088 and 8086. The execution unit (As the EU) is the same for both. As EU is same, the programming instructions are exactly the same for each. Programs written for the 8086 can be run on the 8088 without any changes.
[[File:Block-diagram-of-8086.jpg]]