On a computer the hard drive contains spinning disks. The disks contain tiny magnetic cells which we call 'bits'.Each bit can take one of two different magnetic states (called 0 or 1), or each bit has a binary number system that defines it. A byte is made up of 8 bits. A recording head is able to change the state of each magnetic cell by introducing a particular electrical current to the bit and changing it from 0 to 1 or vice versa. As the disk rotates through the recording head, information we put into the computer is recorded as a series of bits on the hard drive by the recording head.The recording heads stay stationery while the disk rotates through it and the recording heads contain components that can read or write information onto the hard drive.

A particular computer requires 0.5um of length to write a single bit of information. This hard-drive is able to rotate at 7200 revolutions per minute. The recording head is 3.4cm from the center of the hard-drive disk.

A. If a hard-drive has 1TB (terabyte) capacity, how many magnetic cells are contained in the hard-drive?

B. What is the length of all these magnetic cells (in miles) if they were incorporated end to end (instead of in a disk shape)

C. What is the linear velocity of the hard drive in m/s? How does this compare to the speed of a car which is moving at 60mph?

D. What is the time period of this hard drive? How long would it take to write 1 TB of information onto it if this is the rate-limiting step of information transfer?