An operating system supports a paged virtual memory, using a central processor with a cycle time of 1 microsecond. It costs an additional 1 microsecond to access a page other than the current one. Pages have 1000words, and the paging device is a drum that rotates at 3000 revolutions per minute and transfers 1 million words per second. The following statistical measurements were obtained from the system: 1 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.