Once again, the Mac has increased its US market share, according to the latest results from both the Gartner (http://www.gartner.com) IDC (http://www.idc.com) research group. The former has Apple will 9.3% of the US computer market share; the latter says Apple has 8.5%.

Remember: these stats don’t include iPad sales. Neither research group counts the tablet in their personal computer sales even though the iPad is obviously a tablet computer.

According to Gartner, Mac shipments totaled approximately 1.5 million units in the first quarter of 2011, up from 1.3 million in the first quarter of 2010. That’s year-over-year growth of 18.9%.

This places Apple fifth on the list of Gartner’s US computer vendors. It trails HP (26.2% market share with -3.5% year-over-year growth), Dell (22.3%, -12.1% year-over-year growth), Acer (11.3%, -24.9% year-over-year growth) and Toshiba (10.4%, 10.9% year-over-year growth).

Gartner says Apple maintained strong shipment growth, even after the holiday season. The MacBook Pro refresh at the end of February accelerated already strong Mac growth.

According to IDC, Mac shipments totaled approximately 1.4 million units in the first quarter of 2011, up from 1.3 million in the first quarter of 2010. That’s year-over-year growth of 9.6%.

This places Apple fourth on the list of IDC’s US computer vendors. It trails HP (27% market share with -2.4% year-over-year growth), Dell (23.1%, -11.8% year-over-year growth), and Toshiba (10.3%, 10.4% year-over-year growth). IDC places Apple ahead of Acer (8.3% market share; -42.1% year-over-year growth).

— Dennis Sellers