Solution

The correct answer is 12 μs.

Key Points

• Block size = 2000 bytes.
• Each byte transfer in programmed I/O takes 6 CPU cycles.
• CPU clock speed = 1 GHz = 10⁹ cycles/sec.

Step-by-Step Solution

• Step 1: Compute CPU cycles used
• Total cycles = Bytes × Cycles per byte
• = 2000 × 6 = 12000 cycles
• Step 2: Convert cycles to time
• Time per cycle = 1 / 10⁹ sec = 10⁻⁹ sec
• Step 3: Compute total time
• Time = 12000 × 10⁻⁹ sec
• = 1.2 × 10⁻⁵ sec
• Step 4: Convert to microseconds
• 1 μs = 10⁻⁶ sec
• Time = 1.2 × 10⁻⁵ / 10⁻⁶
• = 12 μs

Additional Information

• Programmed I/O keeps CPU busy during full transfer.
• DMA significantly reduces CPU time.