DOS was a rip off (literally ripped off and tweaked for a rush job for IBM)
Actually, wasn't DOS Based on QDOS by Seattle Software Products?
IIRC Microsoft purchased
perpetual legal rights to that OS in 1980 to serve as the basis for the OS that IBM had contracted Microsoft to provide for its PC. For this, Microsoft paid
a one-time fee of $50k to Seattle Software, but didn't tell them ('ostensibly because Microsoft was under an NDA and therefor barred from discussing it) what they wanted it for. Tim Paterson, the founder of Seattle Software and author of QDOS, went to work for Microsoft the following year.
In retrospect, that became one of the shrewdest business deals ever made. But hardly a financial ripoff. $50k was a fairly substantial amount of money back then. Especially in an industry that catered largely to the hobbyist market prior to IBM releasing their PC.
So what about it being a technology ripoff?
Gary Kildall of Digital Research (originally: Intergalactic Digital Research) often claimed that QDOS was "largely lifted" from his operating system CP/M.
Paterson acknowledged he had extensively based QDOS on CP/M, but argued the coding was all his and therefor was a legal functional equivalent of CP/M rather than a copy. Some preliminary and largely unsuccessful legal skirmishes early on led Kildall to believe Digital Research didn't have a leg to stand on if they went to court. So the widely hinted, and eventually threatened, lawsuit never materialized. No software patent trolling or look&feel nonsense back in those days!
In the 80s, the rule of thumb used to be something like if 80% (or more) of your source code was original, your work was considered original. That was because there was a general consensus that software was developed in an "evolutionary fashion, and therefor (of necessity) tended to "incorporate" elements (i.e. algorithms,code snippets, standard routines, etc.) which had been previously written by others.
In the 80s, nobody seriously considered software as being copyrightable because it was regarded as a set of instructions rather than a 'creative' or 'literary' work. Instruction sets are not usually eligible for copyright protection.
And software was not considered patentable for the same reason since it was viewed more as an 'idea' than it was the 'expression' of one. Ideas, by themselves, are not patentable.
There was also a very different 'business view' of software back then.
Most PC system software (particularly the OS) had yet to be considered as separate products. It was usually just thought of as an accessory. If you looked at the PC invoices of the time, you'd often see system software and utility disks all lumped together and called something like Accessory-Std. Software Pack
with a line price that read: included
In the 80s, an OS came bundled with the hardware you bought. Mainframes and minicomputers often had complex and expensive support and licensing schedules. But the big selling point for PC was that it came with an OS which was *SOLD* to the customer
rather than licensed annually. That was a major paradigm shift for the computer industry. It wasn't till much later that the notion of licensing
PC software became the norm. And it was a very hard sell convincing the public (and most courts) that a "shrink-wrap license" you didn't get to read, negotiate over, or personally sign, became legally binding if you unsealed a box. That alone constituted a major breakthrough getting the public to accept that.