A $255-$GB disk has $65,536$ cylinders with $255$ sectors per track and $512$ bytes per sector. How many platters and heads does this disk have? Assuming an average cylinder seek time of $11$msec, average rotational delay of $7$msec. and reading rate of $100M\frac{B}{sec},$ calculate the average time it will take to read $100KB$ from one sector.