You're probably too young to remember the antique known as a typewriter. On some electric versions of this machine, you could hold down the letter X key to type a series of XXXXXXXs—ideal for crossing something out in a contract, for example.
Figure 8-15. How fast do you want your keys to repeat? This control panel also offers a Hardware tab, but you won't go there very often. You'll use it exclusively when you're trying to troubleshoot your keyboard or its driver.