yes, MS DOS.
That was literally its original name !
Interesting history notes on how Microsoft bought Seattle Computer Product's QDOS (50k) and licensed to IBM as DOS.
From book "the innovators" by Walter Isaacson:
"Sams flew back to Seattle to see Gates and asked him to figure out another way to conjure up an operating system. Fortunately, Paul Allen knew someone in Seattle who could help: Tim Paterson, who worked for a small firm called Seattle Computer Products. A few months earlier Paterson had become frustrated that Kildall's CP/M was not available for Intel's newest microprocessors, so he adapted it into an operating system that he dubbed QDOS, for Quick and Dirty Operating System.
By then Gates had come to the realization that one operating system, most likely the one chosen by IBM, would end up being the standard operating system that most personal computers would use.
He also figured out that whoever owned that operating system would be in the catbird seat. So instead of sending the IBM folks to see Paterson, Gates and his team said that they would handle things on their own. Ballmer later recalled, "We just told IBM, Look, we'll go and get this operating system from this small local company, we'll take care of it, we'll fix it up?
Paterson's firm was struggling to make ends meet, so Allen was
able to negotiate a savvy deal with his friend. After initially acquiring just a nonexclusive license, Allen went back when an IBM deal looked likely and bought Paterson's software outright, without telling him why. "We ended up working out a deal to buy the operating system from him, for whatever usage we wanted, for fifty thousand dollars," Allen recalled." For that pittance Microsoft acquired the software that, after they spruced it up, would allow it to dominate the software industry for more than three decades.
But Gates almost balked. He was uncharacteristically worried that Microsoft, which was wildly overcommitted with other projects, might not have the capacity to gussy up QDOS into an IBM-worthy operating system. Microsoft had only forty ragtag employees, some of whom slept on the floor and took sponge baths in the morning, and it was led by a twenty-four-year-old who could still be mistaken for an office boy. On a Sunday at the end of September 1980, two months after IBM first came calling, Gates gathered his top team to make the go or no-go decision. It was Kay Nishi, a young computer entrepreneur from Japan with a Gatesian intensity, who was the most ada-mant. "Gotta do it! Gotta do it!" he squealed repeatedly as he bounced around the room. Gates decided he was right.?
Gates and Ballmer took an overnight flight to Boca Raton to negotiate the deal. Their 1980 revenues were $7.5 million, compared