The storage area of a disk has innermost diameter of 10 cm and outermost…

2004

The storage area of a disk has innermost diameter of 10 cm and outermost diameter of 20 cm. The maximum storage density of the disk is 1400bits/cm. The disk rotates at a speed of 4200 RPM. The main memory of a computer has 64-bit word length and 1µs cycle time. If cycle stealing is used for data transfer from the disk, the percentage of memory cycles stolen for transferring one word is  

Answer: C. 5% — Key idea: use the innermost track (worst-case) to compute the data transfer rate and then find the fraction of memory cycles used. Innermost circumference = π…

  1. A.

    0.5%

  2. B.

    1%

  3. C.

    5%

  4. D.

    10%

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Correct answer: C

Key idea: use the innermost track (worst-case) to compute the data transfer rate and then find the fraction of memory cycles used.

  • Innermost circumference = π × innermost diameter = π × 10 cm ≈ 31.416 cm.

  • Bits per rotation = storage density × circumference = 1400 bits/cm × 31.416 cm ≈ 43,982 bits/rotation.

  • Rotations per second = 4200 RPM / 60 = 70 rps, so data rate ≈ 43,982 × 70 ≈ 3,078,740 bits/s.

  • Words transferred per second = data rate / 64 bits = 3,078,740 / 64 ≈ 48,106 words/s.

  • Memory cycles per second = 1 / (1 µs) = 1,000,000 cycles/s. Fraction stolen = 48,106 / 1,000,000 ≈ 0.048106 = 4.8106%.

Final answer: approximately 4.81%, which rounds to 5%.

Explore the full course: Iocl Engineers Officers Grade A Paper 2

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