Based on Elerath's (2009) article, what are the two main categories of hard disk drive failure? How does SMART technology work, and what does it mean when limits are exceeded?

According to the article the two main categories are known as operational failures and latent defects. Operational failure is a failure where data cannot be written in the hard drive or a data cannot be retrieved from a hard drive or both. The main reason of operational failure is because the read and write heads of the hard disk drive is either losing its track or cannot stay on the track. Moreover, another possibility of having this failure is because the magnetic properties of the hard drive are damaged such as an ESD (electrical static discharge) has happened, it was exposed to high temperature, or there was a...