Global shipments of devices (PCs, tablets, notebooks and mobile phones) are projected to reach 2.4 billion units in 2014, a 4.2 percent increase from 2013, according to Gartner analysts.

As has been the case for at least a decade, sales of desktop PCs are declining. In 2014, overall PC sales (desktop, notebook, ultra-mobiles) will decline just 2.9 percent, after falling nearly 10 percent in 2013, according to Ranjit Atwal, Gartner research director.

But traditional desk-based and notebook PC sales will contract 6.7 percent in 2014 and 5.3 percent in 2015. 

Gartner estimates that sales of tablets will see a relative slowdown in 2014 to reach 256 million units, an increase of 23.9 percent from 2013.

Sales of mobile phones are expected to reach 1.9 billion units in 2014, a 3.1 percent increase from 2013.

Sales of smartphones, which exceeded those of the rest of the market in 2013, will continue to do well, and Gartner estimates that smartphone sales will represent 88 percent of global mobile phone sales by 2018 — up from 66 percent in 2014.

All those trends suggest some “substitution” effects. Notebooks are used instead of desktop PCs. Tablets are used in place of notebooks, and smartphones are used in place of other PC devices.

But one might also say that in many cases the devices are used in different settings, for different reasons. PCs or notebooks are used for complex or voluminous content production. Tablets are used for light content creation, but mostly for content consumption.

Smartphones are used primarily for communications and content consumption, everywhere, while desktops are used at fixed locations, while notebooks are used when users are stationary.

Though it is true that smartphones are device substitutes for PCs in many instances, it also is true that modern computing experiences are sufficiently diverse that a smartphone, phablet or tablet accomplishes many tasks that formerly might have required a PC or notebook.

In other words, applications with high value now are largely content consumption related, with only modest demand for content creation (a tweet, a post, a reply, filling out a form or interacting with a button or hot link).

In that sense, use of various devices does not just represent substitution for PC devices, but the growing range of uses of cloud-based content that are suited to non-PC devices.

Where once only PCs could support such content consumption, now the new devices surface what once was latent demand for content consumption.