- Intel introduced the 8086 processor in 1978, a 16-bit chip that founded the x86 architecture.
- The ALU performs 28 operations including arithmetic, logic, shifts, and BCD adjustments.
- Microcode controls the ALU via a two-step process: first configure the ALU, then retrieve the result.
- The ALU uses a lookup table approach with six control signals to implement various operations.
- The die photo shows the chip partitioned into Bus Interface Unit (BIU) and Execution Unit (EU), with ALU control circuitry highlighted.
- The ALU control circuitry includes latches, PLAs, multiplexers, and flip-flops to decode micro-instructions and instruction opcodes.
- The XI pseudo-operation allows the same microcode to handle multiple machine instructions by substituting the ALU operation from the opcode.
- The 8086's CISC design introduces complexity through special cases like shifts, decimal adjustments, and carry handling.