James M. Spangler, a janitor working in a department store, invented the modern, portable, bagged vacuum in 1907. Soon after perfecting and patenting the idea, he started his own company that produced electric vacuums. (The patents were later purchased by an individual who renamed the company after himself: Hoover.)
Spangler's early prototypes used pillowcases to serve as vacuum bags, and today's bagged vacuum cleaners work much like these early models, but using cloth or paper bags. A fan inside the vacuum creates suction, pulling air in through the intake and pushing it out through an exhaust port. Often, a vacuum has a rotating brush on the bottom that helps dislodge dirt and dust as the vacuum passes over it. This dirt and dust is carried through the intake port, and through the cloth or paper bag, where it remains -- unless it's small enough to slip through holes in the bag. The air, which passes through the bag's holes, continues through the bag and out the exhaust port.
If the bag is full, the vacuum begins to lose suction power. When you change the bag, it normally has a flap that closes as soon as it's removed, preventing dust from escaping. You can then throw away the bag and replace it with a new one.
James Dyson was a man who strongly disliked bagged vacuum cleaners. He set his mind to creating a vacuum cleaner that required no bags and didn't lose suction power as it collected more and more dirt. He finally struck upon a system that worked.
As with a bagged vacuum, bagless vacuums draw in air through an intake valve. However, once your carpet's dirt and dust is inside the vacuum chamber, centrifugal force is used to separate particles from the airstream. These particles are flung outward against the chamber wall, falling into a collection cup as the air leaves the chamber and exits the vacuum through an exhaust port. Aside from the mechanics of the differing dust-collection methods, bagged and bagless vacuums are otherwise similar, and both features can be found on vacuums that span a range of styles and designs.
So why are bagless vacuums popular? Find out in the next section.