The CPU a system having 1 MIPS execution needs 4 machine cycles on an average for executing an instruction. The fifty percent of the cycles use memory bus.…
The CPU a system having 1 MIPS execution needs 4 machine cycles on an average for executing an instruction. The fifty percent of the cycles use memory bus. A memory read/write employs one machine cycle. For execution of the programs, the system utilizes 90 percent of the CPU time. For block data transfer, an IO device in attached to the system while CPU executes the background programs continuously. What is the maximum I/O data transfer rate if programmed I/O data transfer technique is used?
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Correct answer: (D) 250 Kbytes/sec
Explanation
CPU speed is 1 MIPS = 10⁶ instructions per second. With programmed I/O, each byte transferred needs about one instruction-equivalent of 4 machine cycles (status check, branch, read/write data), so the maximum transfer rate = 10⁶ / 4 = 250,000 bytes/sec = 250 Kbytes/sec.