Question

Consider a computer system with DMA support.
The DMA module transfers one 8-bit character in one CPU cycle using cycle stealing. The processor speed is 2 MHz and 0.5% of processor cycles are used for DMA. The data transfer rate of the device is \(\underline{\hspace{2cm}}\) bits per second.

Hint:

In cycle stealing DMA, data rate depends on the fraction of CPU cycles stolen.

Answer 1

Correct Answer: 80000

Processor speed: \[ 2~\text{MHz} = 2 \times 10^6 \text{ cycles/second} \] DMA uses: \[ 0.5% = 0.005 \text{ of total cycles} \] DMA cycles per second: \[ 2 \times 10^6 \times 0.005 = 10{,}000 \text{ cycles/second} \] Each DMA cycle transfers: \[ 8 \text{ bits} \] Hence, data transfer rate: \[ 10{,}000 \times 8 = 80{,}000 \text{ bits/second} \] Final Answer: \[ \boxed{80000} \]