According to IDC, worldwide computer sales are expected to decline by 10.1 per cent in 2013, by far the most severe yearly contraction on record.

On the basis of data from its Worldwide Quarterly PC Tracker,  International Data Corporation (IDC) had already projected a year-on-year fall of 9.7% in PC shipments for 2013, but its most recent figures paint an even gloomier picture for PC vendors.

IDC's data reveals it is the consumer market that has been hardest hit with an annual 15% drop in shipments for 2013. The commercial market has seen a decline of only 5% and this relative stability is explained as being due to a mix of more stable PC investment planning, a smaller impact from tablets, and replacements of Windows XP systems before the end of support in April 2014

Looking further into the future, IDC forecasts that shipments of portable and desktop PCs combined, will decline by an additional 3.8% in 2014 and hardly recovering in 2015, when total PC shipments will be barely above 300 million, which is back to 2008 levels.

On a worldwide basis desktop PCs currently account for 43% iof PC shipments, but as this table shows, in emerging markets desktop PCs account for 47% compared to 38% in mature markets.

Commenting on the research, Jay Chou, senior analyst at IDC, said:

"Perhaps the chief concern for future PC demand is a lack of reasons to replace an older system. While IDC research finds that the PC still remains the primary computing device – for example, PCs are used more hours per day than tablets or phones – PC usage is nonetheless declining each year as more devices become available. And despite industry efforts, PC usage has not moved significantly beyond consumption and productivity tasks to differentiate PCs from other devices. As a result, PC lifespans continue to increase, thereby limiting market growth."

In other words there isn't a really good reason to buy a replacement PC the current one will do the job. What this means for software developers is difficult to predict because while the desktop PC represents a big market old machines tend to have the software they need to be useful.