More bad news for struggling makers of personal computers: a new forecast Tuesday suggests sales will fall another 7.8 percent in 2013 as buyers delay PC purchases or choose an alternative device.

The research firm IDC said the drop is likely to be steeper than its previous prediction, and come on the heels of a four percent decline in 2012.

The updated forecast reflects a huge drop in volume in the first quarter of 2013 and consumer reaction to new PCs using Windows 8, including more thin, convertible, touch, and slate models.

"Many users are realizing that everyday computing, such as accessing the Web, connecting to social media, sending emails, as well as using a variety of apps, doesn't require a lot of computing power or local storage," said IDC analyst Loren Loverde.

These users "have not necessarily given up on PCs as a platform for computing when a more robust environment is needed, but this takes a smaller share of computing time, and users are making do with older systems," Loverde added.

IDC said last month that worldwide sales of PCs slid 13.9 percent in the first quarter of 2013, the worst contraction since it began tracking the market in 1994.

IDC said it expects to see some improvement in 2014, particularly in the commercial segment, as support for Windows XP expires.

The research firm said in a separate report that tablet sales are expected to grow 58.7 percent in 2013 to 229.3 million units.

This would bring tablet shipments above those of portable PCs this year. And IDC said it expects tablet shipments to outpace the entire PC market by 2015.

"What started as a sign of tough economic times has quickly shifted to a change in the global computing paradigm with mobile being the primary benefactor," said IDC's Ryan Reith.

"Tablets surpassing portables in 2013, and total PCs in 2015, marks a significant change in consumer attitudes about compute devices and the applications and ecosystems that power them."