Background checks are basically where you take a bunch of public records (from the likes of courthouses and police stations) and actually weave them into a central file, or report, based around someone. The reliability and accuracy of the background report all depend on the company where you got it from, and how up-to-date their information is. You can also run an instant background checks online on anyone.
Back in the times before the Internet, performing background checks was a time-consuming and hit-and-miss affair. Not only did it take several days to get access to someone's background information, but you were almost never given the right information the first time. This is because, before the Internet, background check companies had to work with paper-based systems.
This meant that each time you wanted to find out someone's details, the company had to check out all the local government buildings and find the pieces of paper with the person's details. This took a very long time and since there are so many people with the same name, background reports often got confused and information was scattered all over the place.
Luckily, now there are a group of new-age background check companies, who are making instant background checks possible. Companies now let you find out someone's background information just from the comfort of your armchair in seconds. They work by putting all the public records onto virtual files. They then let you search for the people they have records for, and when you select one, they compile a background check on screen for you. It all takes a few seconds because it's all virtual and automated.