The 8086's microcode ROM holds 512 micro-instructions, each 21 bits wide. The microcode engine is assisted by two smaller ROMs: the "Group Decode ROM" to categorize machine instructions, and the "Translation ROM" to branch to microcode subroutines for address calculation and other roles.
See: [https://www.righto.com/2022/11/how-8086-processors-microcode-engine.html How the 8086 processor's microcode engine works] [https://righto.com/8086/groupRom.html Group Decode ROM viewer]
== Pipeline Design ==