Below, I am providing a link to the site for Windows 8.  This is an operating system that was released for general availability just over one year ago (late October of 2012).  This operating system shows how demand curves can be shifted in a variety of ways.

One determinant of demand is the price or the prevalence of complementary goods.  Complementary goods are goods that can be used in conjunction with one another.  If the price of one such good goes down, or if the prevalence of that good goes up, the demand for the other complementary good rises.  In the case of Windows 8, this is an operating system that is made largely with touch screen tablets and other mobile devices in mind.  A few years ago, such devices were not very prevalent and so older Windows operating systems such as Windows 7 were in greater demand.  In recent years, mobile devices have become very prevalent and therefore the demand curve for a system such as Windows 8 moved to the right.

Conversely, the launch of Windows 8 shows how competing goods can affect one another’s demand curves.  Windows 8 is in competition with previous Windows operating systems such as Windows 7.  When Windows 8 was launched, Windows 7 faced more competition than it previously had.  Therefore, its demand curve moved to the left.

Finally, we can say that consumer tastes can shift demand curves one way or the other.  Many computer users were not completely happy with Windows 8.  They felt that it was too different from previous versions of Windows.  Therefore, the demand curve for Windows 8 moved to the left and Microsoft has just released an update, Windows 8.1, that is meant to cater to consumer tastes and move the demand curve for Windows 8/8.1 back to the right.