Consider a computer with a 4 MHz processor. Its DMA controller can transfer 8…
2024
Consider a computer with a 4 MHz processor. Its DMA controller can transfer 8 bytes in 1 cycle from a device to main memory through cycle stealing at regular intervals. Which one of the following is the data transfer rate (in bits per second) of the DMA controller if 1% of the processor cycles are used for DMA?
- A.
2,56,000
- B.
3,200
- C.
25,60,000
- D.
32,000
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Correct answer: C
Key idea: find the number of DMA cycles per second, multiply by bytes per cycle, then convert bytes to bits.
Step 1: Total processor cycles = 4 MHz = 4,000,000 cycles/s. DMA uses 1% of cycles → 0.01 × 4,000,000 = 40,000 DMA cycles/s.
Step 2: Each DMA cycle transfers 8 bytes, so bytes per second = 40,000 × 8 = 320,000 bytes/s.
Step 3: Convert bytes to bits: 320,000 × 8 = 2,560,000 bits/s.
Answer: 2,560,000 bits per second (the option shown as 25,60,000).
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