InClassActivity17-sol - Activity#17(Solution 11:09 PM...

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ECSE-2660 Computer Architecture, Networks, & Operating Systems, Spring 2003 Page 1 of 2 Activity #17 (Solution) 3/25/2003 11:09 PM Activity 17.1 I/O service 1. Consider a processor with a 750MHz clock rate, and a hard disk that transfers data in 16 byte chunks with a transfer rate of 12 MB/sec. 1a. (10 points) Assume the processor uses polling and that each polling operation (transferring to the polling routine, accessing the device, restarting the user program) takes 500 clock cycles. Assume you poll often enough so that no data is ever lost. What is the fraction of the CPU time consumed by polling? We must poll at the rate = sec / 432 , 786 / 16 sec / 12 transfer transfer byte MB = Cycles per sec for polling = 786,432 x 500 = 393.216 x 10^6 Fraction of the CPU = % 43 . 52 6 ^ 10 750 6 ^ 10 216 . 393 = x x Grading: 3 pts for each part, 2 minimum. 1b. (10 points) Assume we use interrupt-driven I/O and the overhead for each transfer is 425 clock cycles. What is the fraction of the CPU time consumed if the disk is transferring data 20% of the time? Cycles per sec for disk = 786,432 x 425 = 334.2336 x 10^6 Fraction of the CPU consumed with constant usage = % 56 . 44 6 ^ 10 750 6 ^ 10 2336 . 334 = × × For 20% average use = 44.56% x 20% = 8.9% Grading: 3 pts for each part, 2 minimum. 1c. (10 points) Suppose we are using DMA. Assume that the initial setup of a DMA transfer takes 700 clock cycles for
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This note was uploaded on 04/25/2010 for the course ECSE ecse-2340 taught by Professor Wozny during the Spring '09 term at Rensselaer Polytechnic Institute.

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InClassActivity17-sol - Activity#17(Solution 11:09 PM...

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