Explain the operation of IRET instruction.  What memory locations contain the vector for an INT 34 instruction?

The Interrupt return (IRET) instruction is utilized only along with software or hardware interrupt service procedures. When an IRET instruction executes, this stores the contents of I and T from the stack. It is important since it preserves the state of the flag bits. If interrupts were enabled before an interrupt service process, they automatically re-enabled through the IRET instruction since this restores the flag register.

Interrupt no. 20-FF are stored at an address 80 - 3FFH.