SANTA CLARA, CA – Tablet PCs are taking a bigger bite out of the mobile PC market, with shipments now making up 25.5% of all mobile PCs in 2011, says NPD DisplaySearch.

Tablets grew 256% year-over-year to 72.7 million units, as strong demand in the third quarter appeared to be a prelude to equally vigorous buying patterns in the fourth, says the research firm.

Introductions of significantly competitive new devices in the fourth quarter, strong demand for incumbents, and additional distribution channels have been catalysts for accelerated tablet PC shipment growth.

NPD DisplaySearch has slightly lowered its notebook PC shipment forecast in 2011 to 187.5 million units, up 12% year-over-year.

Mini-note PC shipments are expected to reach 25.2 million units, up 20% compared to the same period in 2010. Overall mobile PC shipments in 2011 are projected to reach 285.4 million units, up 31% year-over-year.

By 2017, notebook PC shipments are forecast to reach 432 million units, and tablet PC shipments are projected to reach 383.3 million units.

Ultrabooks are an emerging form factor that is expected to contribute to demand in later years of the forecast. Demand for ultrabooks will be driven by consumer interest in sleek design and convenience like instant-on and long battery life, says the firm. For the next two years, the premium price points of Ultrabooks will temper demand, and there may be some supply limitations in production of displays thin enough for Ultrabooks.

Tablet PC shipments will be driven by increasingly powerful multi-core processors, mature operating systems, growing application libraries, and higher resolution panels. NPD DisplaySearch forecasts that tablet PCs with 250 to 300 pixel per inch panels will make up nearly 25% of shipments in 2012.

Mobile PC shipments into emerging regions are growing, with 2011 shipments projected to be 138 million units, up 48% year-over-year, and increasing to 452.8 million by 2017. Mobile PC shipments into mature regions are estimated to reach 147.5 million units in 2011 and grow to 371.6 million units by 2017.

Mobile PC shipments will be up in late 2012 and 2013 with the introduction of Microsoft’s Windows 8 operating system and new mobile processors from Intel.