UGC NET CSE | Junet 2015 | Part 3 | Question: 5

Question

The CPU of a system having 1 MIPS execution rate 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% of the CPU time. For block data transfer, an IO device is attached to the system while CPU executes the background programs continuously. What is the maximum IO data transfer rate if programmed IO data transfer technique is used?

• A. 500 Kbytes/sec
• B. 2.2 Mbytes/sec
• C. 125 Kbytes/sec
• D. 250 Kbytes/sec

Answer 1

ans should be D 

CPU speed 1MIPS=10^6 instruction per sec

1 Cpu instruction =4 machine cycles(Avg)

1 memory read/access = 1 machine cycle

CPU utilization =90%

Programmed I/O

each byte transfer requires 4 cycles (instructions)

in status

check status

Branch 

Read/Write data

max data transfer rate CPU speed /4 = 10^6/4=250 kbytes/sec

Answer 2

It's not 4 cycles which means 1 instruction=1 micro sec hence 1 byte in 1 microsecond but it needs 4 instr. time. 1 mic sec /4