CO-Grand Test 1-Q14

+1 vote

A computer consists of a processor and an I/O device D connected to main memory M via a shared bus with a data bus width of one word. The processor can execute a maximum of 10^7 instructions per second. An average instruction requires five machine cycles, three of which use the memory bus. A memory read or write operation uses one machine cycle. Suppose that the processor is continuously executing “background” programs that require 99% of its instruction execution rate but not any I/O instructions. Assume that one processor cycle equals one bus cycle. Now suppose the I/O device is to be used to transfer very large blocks of data between M and D. If programmed I/O is used and each one-word I/O transfer requires the processor to execute two instructions, estimate the maximum I/O data-transfer rate, in words per second, possible through D.

asked Jun 25 in Computer Organization by gbeditor (11,310 points)
reshown Jun 26 by gbeditor

2 Answers

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Best answer

The processor can execute maximum = 10^7 instructions/sec

background programs require execution rate but not I/O = 99%

so I/O program requires = 1%

so,

10000000 X 0.01 = 100000 instructions/sec

but each word requires the processor to execute 2 instructions 

1 word \longrightarrow 2 instructions

1 instructions \longrightarrow 0.5 instructions

Hence, 100000X 0.5 = 50000 words/sec

answered Jul 2 by gbmentor (35,970 points)
0 votes

The processor can execute maximum = 10^6 instructions/sec

background programs require execution rate but not I/O = 99%

so I/O program requires = 1%

so,

1000000 X 0.01 = 100000 instructions/sec

but each word requires the processor to execute 2 instructions 

1 word \longrightarrow 2 instructions

1 instructions \longrightarrow 0.5 instructions

Hence, 100000X 0.5 = 50000 words/sec

answered Jun 26 by 23rishiyadavpro20 (6,590 points)
edited Jul 2 by 23rishiyadavpro20
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