After 2 decades of continual growth in sales of PCs, indicators are beginning to show a worldwide slowdown. The primary cause of this change in demand appears to be a growth in demand for tablets and smartphones and an increase in the number of people purchasing these as genuine substitutes for an old-style laptop or desktop computer.
PC manufacturers have tried to hit back by increasing the use of touchscreens and even creating hybrid devices that allow users to detach screens and use them as a tablet-like device. Microsoft, dependent on the success of the PC market, has brought in a new version of Windows (v8) to bring a little life back to the computer experience. All of these changes do not appear to have had a great affect (although sales in the USA continue to be bouyant).
This link will take you to an article from the Wall Street Journal showing some facts and figures.
Follow this link for a resource that asks students to draw shifting demand and supply curves to illustrate what is happening to sales of PCs and tablets.