Question

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 1400 bits/cm. The disk rotates at a speed of 4200 RPM. The main memory of a computer has 64-bit word length and 1$\mu$s cycle time. If cycle stealing is used for data transfer from the disk, the percentage of memory cycles stolen for transferring one word is

• A. 10%
• B. 5%
• C. 0.5%
• D. 1%

Answer 1

The correct option is B 5%

$Thecapacityoftrack=\pi \times d\times Density$
$=3.14\times 2^{10}\times 1400bits=14000\pi bits$

$4200rotation=60sec$
$So,1rotationtime=\frac{60}{4200}=\frac{1}{7}sec$

$DMAcontrollertransfer64bits=1\mu sec$

$In1sec=64\times {10}^{6}bits$

$In1secthediskcanread=\frac{14000\pi }{\frac{1}{70}}$

$=3.08\times {10}^{6}bits$

$Totalmemorycyclestolen=\frac{3.08\times {10}^8}{64\times {10}^6}$

$=5\%$