Block Diagram of 8086

Introduction of 8086:

  • The 8086 was the first 16-bit Microprocessor to be introduced by Intel Corporation. It is designed to be upwardly compatible with the older 8080/8085 series of 8-bit microprocessors. The upward compatibility allows programs written for the 8080/8085 to be easily converted to run on the 8086.

  • The word 16-bit means that its arithmetic logical unit, internal registers, and most of its instructions are designed to work with 16-bit binary words. The 8086 has a 16-bit data bus, so it can read data form or write data to memory and ports either 16-bits or 8- bits at a time.

  • The 8086 has a 20-bit address bus, so it can address any one of 220 or 1,048,576 memory locations. Each of the 1,048,576 memory addresses of the 8086 represents a byte-wide location. Words will be stored in two consecutive memory locations. If the first byte of a word is at an even address, the 8086 can read the entire word in one operation. If the first byte of the word is at an odd address, the 8086 will read the first byte of the word in one operation, and the second byte in another operation.


  • The Fetch and Execution are implemented by two process units inside CPU:

  • Bus Interface Unit (BIU) fetches instructions from memory, passes the instruction to the instruction stream byte queue and starts to fetch the next instruction immediately.

  • Execution Unit (EU) removes instructions from the instruction queue.

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