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32. To the extent that developers begin writing attractive applications that rely solely on servers or middleware instead of PC operating systems, the applications barrier to entry could erode. As the Court finds above, however, it remains to be seen whether server? or middleware?based development will flourish at all. Even if such development were already flourishing, it would be several years before the applications barrier eroded enough to clear the way for the relatively rapid emergence of a viable alternative to incumbent Intel?compatible PC operating systems. It is highly unlikely, then, that a firm not already marketing an Intel?compatible PC operating system could begin marketing one that would, in less than a few years, present a significant percentage of consumers with a viable alternative to incumbents.

33. Microsoft enjoys so much power in the market for Intel?compatible PC operating systems that if it wished to exercise this power solely in terms of price, it could charge a price for Windows substantially above that which could be charged in a competitive market. Moreover, it could do so for a significant period of time without losing an unacceptable amount of business to competitors. In other words, Microsoft enjoys monopoly power in the relevant market.

34. Viewed together, three main facts indicate that Microsoft enjoys monopoly power. First, Microsoft's share of the market for Intel?compatible PC operating systems is extremely large and stable. Second, Microsoft's dominant market share is protected by a high barrier to entry. Third, and largely as a result of that barrier, Microsoft's customers lack a commercially viable alternative to Windows.

35. Microsoft possesses a dominant, persistent, and increasing share of the world?wide market for Intel?compatible PC operating systems. Every year for the last decade, Microsoft's share of the market for Intel?compatible PC operating systems has stood above ninety percent. For the last couple of years the figure has been at least ninety?five percent, and analysts project that the share will climb even higher over the next few years. Even if Apple's Mac OS were included in the relevant market, Microsoft's share would still stand well above eighty percent.

39. Consumer demand for Windows enjoys positive network effects. A positive network effect is a phenomenon by which the attractiveness of a product increases with the number of people using it. The fact that there is a multitude of people using Windows makes the product more attractive to consumers. The large installed base attracts corporate customers who want to use an operating system that new employees are already likely to know how to use, and it attracts academic consumers who want to use software that will allow them to share files easily with colleagues at other institutions. The main reason that demand for Windows experiences positive network effects, however, is that the size of Windows' installed base impels ISVs to write applications first and foremost to Windows, thereby ensuring a large body of applications from which consumers can choose. The large body of applications thus reinforces demand for Windows, augmenting Microsoft's dominant position and thereby perpetuating ISV incentives to write applications principally for Windows. This self?reinforcing cycle is often referred to as a "positive feedback loop."

40. What for Microsoft is a positive feedback loop is for would?be competitors a vicious cycle. For just as Microsoft's large market share creates incentives for ISVs to develop applications first and foremost for Windows, the small or non?existent market share of an aspiring competitor makes it prohibitively expensive for the aspirant to develop its PC operating system into an acceptable substitute for Windows. To provide a viable substitute for Windows, another PC operating system would need a large and varied enough base of compatible applications to reassure consumers that their interests in variety, choice, and currency would be met to more?or?less the same extent as if they chose Windows. Even if the contender attracted several thousand compatible applications, it would still look like a gamble from the consumer's perspective next to Windows, which supports over 70,000 applications. The amount it would cost an operating system vendor to create that many applications is prohibitively large. Therefore, in order to ensure the availability of a set of applications comparable to that available for Windows, a potential rival would need to induce a very large number of ISVs to write to its operating system.

45. The experiences of IBM and Apple, Microsoft's most significant operating system rivals in the mid? and late 1990s, confirm the strength of the applications barrier to entry.