Consider a three word machine instruction $$ADD$$ $$A$$ $$\left[ {{R_0}} \right],\,@\,B$$

The first operand (destination) ''$$A$$ $$\left[ {{R_0}} \right]''$$ uses indexed addressing mode with $${{R_0}}$$ as the index register. The second operand (source) $$''@B''$$ used indirect addressing mode. $$A$$ and $$B$$ are memory addresses residing at the second and the third words, respectively. The first word of the instruction specific the opcode, the index register designation and the source and destination addressing modes. During execution of $$ADD$$ instruction, the two operands are added and stored in the destination (first operand).

The number of memory cycles needed during the execution cycle of the instruction is

Normally user programs are prevented from handling $${\rm I}/O$$ directly by $${\rm I}/O$$ instructions in them. For $$CPUs$$ having explicit $${\rm I}/O$$ instructions, such $${\rm I}/O$$ protection is ensured by having the $${\rm I}/O$$ instructions privileged. In a $$CPU$$ with memory mapped $${\rm I}/O$$, there is no explicit $${\rm I}/O$$ instruction. Which one of the following is true for a $$CPU$$ with memory mapped $${\rm I}/O$$ ?

A device with data transfer rate $$10$$ $$KB/sec$$ is connected to a $$CPU.$$ Data is transferred byte-wise. Let the interrupt overhead be $$4$$ $$\mu \sec $$. The byte transfer time between the device interface register and $$CPU$$ or memory is negligible. What is the minimum performance gain of operating the device under interrupt mode over operating it under program controlIed mode?

Consider the disk drive with the following specifications $$16$$ surfaces, $$512$$ tracks/surface, $$512$$ sectors/track, $$1$$ $$KB/sector$$, rotation speed $$3000$$ $$rpm.$$ The disk is operated in cycle stealing mode whereby whenever one byte word is ready it is sent to memory; similarly, for writing, the disk interface reads a $$4$$ byte word from the memory in each $$DMA$$ cycle. Memory cycle time is $$40$$ $$nsec$$. The maximum percentage of time that the $$CPU$$ gets blocked during $$DMA$$ operation is