# 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%

reshown Jun 26

+1 vote

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

so

Slowed down by

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

now I am getting the option A

answered Jun 26 by (6,850 points)
edited Jul 24
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%
corrected........