A processor is fetching instructions at the rate of 1 MIPS. A DMA module is used to transfer characters to RAM from a device transmitting at 9600 bps. How much time will the processor be slowed down due to DMA activity?
- A. 9.6 ms
- B. 4.8 ms
- C. 2.4 ms
- D. 1.2 ms
Answer: D. 1.2 ms
Explanation: 1 MIPS = $10^6$ instructions/sec. 9600 bps. Assuming 1 character = 8 bits? Or async? Usually 1 char = 1 byte. 9600 bits/sec = 1200 bytes/sec. DMA steals cycles. If 1 cycle per byte? Processor speed 10^6 cycles/sec? 1200 cycles stolen. Slowdown = 1200/10^6 = 0.0012 sec = 1.2 ms.