A typewriter does not have computer memory. As with writing with a pen, it is difficult to correct mistakes. One advantage is that many of them are not electrical, so you do not need to plug them in. Hackers cannot see what you have typed. On many typewriters, a separate type element (called a typebar) corresponds to each key. The first commercial typewriters were introduced in 1874. They did not become common in offices until after the mid-1880s. 