retagged by
857 views
3 votes
3 votes
A $DMA$ module is transferring bytes to memory using cycle stealing mode from a device transmitting at $16 KB/s$. The processor is fetching instructions at the rate of $1 MB/s$. The percentage by which the processor will be slowed down due to the $DMA$ activity is ______.
retagged by

2 Answers

Best answer
0 votes
0 votes
Device transfers 1 byte in 61 microsec. 16kB / sec
Memory operation transfers 1 Byte in 1microsec.  1MB / sec.
%CPU idle time = 1/(1+61) = 1.6%
selected by
3 votes
3 votes

Suppose each intruction size is 1  Byte, So, if DMA doesn't interrupt CPU then it will fetch $10^6$ instructions in one second.

To transfer 1 Byte $= \frac{1}{16K} = 62.5$ Microseconds

So DMA will interrupt CPU $\frac{1Sec}{62.5 Micro Sec}=16000 times$

When CPU can fetch $10^6$ instructions in 1 second, it will fetch now $10^6-16000 = 984000$ instructions only.

Hence CPU is slowed down by $=\frac{16000}{10^6} = 0.016 = 1.6\text{%}$

Answer:

Related questions

4 votes
4 votes
2 answers
2
Bikram asked Jan 24, 2017
469 views
The value of the expression $1 - 6 + 2 - 7 + 3 - 8 +$……… to $100$ terms is __________.
5 votes
5 votes
2 answers
4
Bikram asked Jan 24, 2017
804 views
$HCF$ of two numbers is $23$ and other two factors of their $LCM$ are $13 $&$ 14$. The largest of two numbers is _________