Consider a hypothetical processor with an instruction of type $$LW$$ $$R1, 20(R2),$$ which during execution reads a $$32$$-bit word from memory and stores it in a $$32$$-bit register $$R1.$$ The effective address of the memory location is obtained by the addition of a constant $$20$$ and the contents of register $$R2.$$ Which of the following best reflects the addressing mode implemented by this instruction for the operand in memory?

On a non-pipelined sequential processor, a program segment, which is a part of the interrupt service routine, is given to transfer $$500$$ bytes from an $${\rm I}/O$$ device to memory. Initialize the address register Initialize the count to $$500$$

$$LOOP:$$ Load a byte from device Store in memory at address given by address register
Increment the address register
Decrement the count
If count! $$=0$$ go to $$LOOP$$

Assume that each statement in this program is equivalent to a machine instruction which takes one clock cycle to execute if it is a non load/store instruction. The load-store instructions take two clock cycles to execute.

The designer of the system also has an alternate approach of using the $$DMA$$ controller to implement the same transfer. The $$DMA$$ controller requires $$20$$ clock cycles for initialization and other overheads. Each $$DMA$$ transfer cycle takes two clock cycles to transfer one byte of data from the device to the memory.

What is the approximate speed up when the $$DMA$$ controller based design is used in place of the interrupt driven program based input- output?

Which of the following must be true for the $$RFE$$ (Return From Exception) instruction on a general purpose processor?
$$1.$$ It must be a trap instruction
$$2.$$ It must be a privileged instruction
$$3.$$ An exception cannot be allowed to occur during execution of an $$RFE$$ instruction.

Which of the following is/are true of the auto increment addressing mode?
$$1.$$ It is useful in creating self relocating code
$$2.$$ If it is included in an Instruction Set Architecture, then an additional $$ALU$$ is required for effective address calculation
$$3.$$ The amount of increment depends on the size of the data item accessed.