Computer monitors are electrical visual displays that connect to the computer tower. The first computer monitor was invented in 1987 by German physicist Karl Ferdinand. However, that wasn't a compute monitor as such- it was a calculator screen! However, monitors have developed a lot since then, to the point where almost every household has at least one.
Nowadays, in some computers (like the iMac) the computer tower is inside the monitor, forming an all in one computer- a bit different to the original computers!
The original computer was a calculator screen, but over the years they were modified and improved. Some schools including the RGS in Guildford had a computer in the 1980s that had to be fed little punch cards to keep the monitor going!