Merlin, I may have gotten my facts wrong. I recall playing one of the Rainbow 6 FPS (First Person Shooter) games a few years back, and for one episode in an urban multi-story building setting I recall having a choice of several machine guns, a SAW (Squad Automatic Weapon) or another big capacity gun. My (perhaps faulty) recollection was that at least one of them had a big round magazine, not a belt, of either 100 or 200 rounds.Jim, there are all kinds of machine guns around the world and most of what I know about them is from being in the U.S. Army 40 years ago. Most machine guns then were M60's (7.62 mm), with many mounted on helicopters. It started being replaced by the M240 and M249 Squad Automatic Weapon (SAW, 5.56 mm) in the late 1970's and 1980's. The M60 and M240 are belt-fed. The M249 is belt-fed or magazine-fed. I'd guess it's mostly used as belt-fed. From the same article:
"The M249 is an air-cooled, gas-operated, fully-automatic-only firearm that fires from an open bolt position. It can accept belts of linked 5.56x45mm NATO (.223) ammunition through the top-mounted feed tray or M16-type magazines through the side-mounted port. The latter allows a SAW gunner to use riflemens' magazines in an emergency if he runs out of belted ammunition, though this often causes jams as the magazine spring cannot adequately keep up with the weapon's high rate of fire."
There are two general kinds of magazines - box and drum. See here for some pictures of the former. Box magazines usually hold 20 or 30 rounds, although the article says 40-round ones do exist. Drum magazines ordinarily hold 50 to 100 rounds. It would not depend on a spring like a box magazine does. It seems drum magazines are rare, unless talking about Prohibition-era gangsters. See here.
So generally speaking 200 rounds implies a belt. Of course, the maker of a video game or movie can be creative and ignore practical reality. I vaguely recall in the Rambo movies that Rambo had the ammo belts wrapped around his body. Despite being twisted and constrained like that, somehow the ammo belt fed the gun without a glitch while he fired on automatic. :-)