One was used by Jesse ventura's character in Predator. This Internet Movie Firarms Database article describes the gun used in Predator, and also states that U.S. special forces tested a hand held model in the 1970's.
Nicknamed "Painless", a hand-held M134 Minigun is the main weapon carried by Blain (Jesse Ventura). This particular weapon was modified for handheld use with an M60 handguard assembly (installed backwards) and a rear pistol grip which is taken from normal (at the time) Minigun spade grips. The grips are attached to the weapon by a custom Y-frame with an M16-style carry handle that mounts to the weapon's recoil absorbers. The weapon was powered by an electric cable hidden off camera and fired blank rounds to ease the recoil force; in addition, the rate of fire is substantially decreased from the normal 6,000 RPM to 1,250 RPM. There are several reasons for this; to ease recoil, save on ammunition, and because director John McTiernan wanted the barrels to be visibly turning rather than a blur. It is believed in real life a similar weapon was tested by US special forces in the 1970s but found to be impractical.
THis IMFDB article discusses the min-gun used in T2, and its differences from the one in Predator.
But the main article on the gun itself clearly states that such a weapon couldn't be operated by a human. So it is entirely a work of fiction.
A distinctive invention of fiction is the hand-held M134 minigun, a concept which was popularized by the film Predator. Physically demanding even for a slowed-down minigun firing blanks, such a weapon would be impossible for a human being to either carry or operate. This fact has not stopped it appearing frequently in other works, especially in video games. Generally such depictions will totally ignore the weapon's need for external power, and sometimes even forget it requires a source of ammunition.
So, yes, a gun like that has been used in fictional universes, and was at least attempted by the military. But it isn't feasible for a person to operate.
Updated to add: If I ever get my hands on one, I'm stockpiling it, whether it's practical or not!
Update 2: Sarah Connor has seen a Terminator at bad breath distance. She knows they exist and knows that small arms are not very effective at stopping them - you need as much firepower as possible. She believes that more are coming once Skynet becomes self aware
. So Sarah would stockpile a hand held nuke if they existed and she could get one.
She has obviously has had previous contact with Enrique and has had an influence on his buying habits.
But even absent Sarah's influence, if he ever acquired one, he would probably keep it until a buyer came along. It is unique and would probably bring several thousand dollars from the right buyer. He would not care if the buyer could use it effectively.
And lastly, the handles attached to the gun don't necessarily prevent it from being mounted to a vehicle and used in the normal way, so it is still a useful weapon.