The first caps lock key was introduced in the Remington typewriter in the year 1878.
It was known as the shift key. Shift lock was added to the later models of the typewriter in 1914. The first PC with a key board was equipped with the same shift lock to represent capital letters. In the Xerox Alto computers introduced in 1973, it was known as lock.
By 1984 the IBM computers were launched and in their keyboards the caps lock was first used by its name. To this day, all computers irespective of their make use caps lock.
Words written in capitals are synonymous with shouting and hence considered rude. Even celebrities like Oprah Winfrey have fallen prey to the use of caps on their social networking sites.