The Market Structure of Microsoft Microsoft is the undisputed leader in the market for operating systems (Sheremata 1997). The Microsoft Corporation has produced the vast majority of operating systems for all personal computers (PCs); moreover, operating systems that Microsoft has created are Windows95, Windows 3.1, and DOS. They also have produced the leading spreadsheet and word processors for both Windows and Macintosh operating systems. They own 85% of the market share with their office software Word, Excel, Powerpoint, Microsoft Exchange, and Microsoft Access. Not surprisingly, most of us hav