What is the difference between a direct and an indirect address instruction? How many refrences to memory are needed for each type of instruction to bring an operand into a processor register?

Question. What is the difference between a direct and an indirect address instruction? How many references to memory are needed for each type of instruction to bring an operand into a processor register

Answer.

Direct Address Instruction : In Direct address instruction second part of the instruction code implies memory address of operand.

Indirect Address Instruction: In this type of instruction code, second part of instruction code implies effective address of operand.

Have a look at this figure , you will get it.

Part B : 
A direct address instruction needs two references to memory: 
(1) Read instruction; (2) Read operand.
An indirect address instruction needs three references to memory:
(1) Read instruction; (2) Read effective address; (3) Read operand.