DOS
DOS primarily consists of Microsoft's MS-DOS and a rebranded version under the name IBM PC DOS , both of which were introduced in 1981 . 
<triplet> DOS <subj> 1981 <obj> inception <triplet> MS-DOS <subj> DOS <obj> instance of <subj> Microsoft <obj> developer <subj> DOS <obj> instance of <subj> DOS <obj> instance of <triplet> DOS <subj> 1981 <obj> inception <triplet> IBM PC DOS <subj> DOS <obj> instance of <subj> MS-DOS <obj> based on <subj> DOS <obj> instance of <subj> DOS <obj> instance of <triplet> DOS <subj> 1981 <obj> inception