An operating system supports a paged virtual memory. The central processor has a cycle time of $1$ microsecond. It costs an additional 1 microsecond to access a page other than the current one. Pages have $1,000$ words, and the paging device is a drum that rotates at $3,000$ revolutions per minute and transfers $1$ million words per second. The following statistical measurements were obtained from the system:
• $One$ percent of all instructions executed accessed a page other than the current page.
• Of the instructions that accessed another page, $80$ percent accessed a page already in memory.
• When a new page was required, the replaced page was modified $50$ percent of the time.
Calculate the effective instruction time on this system, assuming that the system is running one process only and that the processor is idle during drum transfers.
