Preface: This question does in part intersect with Use of undocumented opcodes, but targets especially the 8086 instruction handling.
I was reading Tanenbaum's "Operating Systems, Design and Implementation" 3rd edition (The MINIX Book), where I encountered the following quote that surprised me:
For instance, the 8086 and 8088 processors do not support detection of illegal instruction operation codes, but this capability is available on the 286 and above, which trap on an attempt to execute an illegal opcode.
What did the 8086 and 8088 do when it an encountered an illegal instruction?
