CO-Grand Test 1-Q15

+1 vote

A DMA module is transferring characters to memory using cycle stealing, from a device transmitting at 240 Kbps. The processor is fetching instructions at the rate of 10^6  instructions per second. By how much will the processor be slowed down due to the DMA activity?

(A) 24 %

(B) 18%

(C) 12%

(D) 16%

asked Jun 25, 2019 in Computer Organization by gbeditor (44,560 points)
reshown Jun 26, 2019 by gbeditor

1 Answer

+1 vote
Best answer

Cycle stealing method: DMA steal for 1 transfer unit (our case character or byte)

240 X 1000 bits  \longrightarrow 1 sec

30X1000 bytes (or characters) \longrightarrow 1 sec

DMA asks CPU for 30000 times

CPU slowed down by

\frac{30000}{10^6}\times 100 \% = 3\%

But there is no option

If we assume 240 KBps then 

240 X 1000 bytes(or characters)  \longrightarrow 1 sec


Slowed down by 

\frac{240000}{10^6}\times 100 \% = 24\%

now I am getting the option A

answered Jun 26, 2019 by 23rishiyadavpro20 (7,210 points)
edited Jul 24, 2019 by 23rishiyadavpro20
But my doubt is "In Kbps b is bytes or there is a mistake in question"
So the right value is 30% I guess
(30000/10^6)*100= 3% not 30%
Could you explain the answer in detail
 Why you used (3000/(10^6))*100
(Time taken by DMA/ Total Time) X 100 @gvsaikmrpro20