El Segundo, Calif . - Tablet PCs are starting to have an impact on computer sales as IHS iSuppli recorded a slight dip in unit shipments for the first quarter of 2011.

The research firm found PC shipments for that period fell 0.3 percent to 81.3 million from 81.6 million during the first quarter of 2011.

In addition, IHS found three of the top five PC shippers suffered a fall off with Acer leading the pack dropping 20.4 percent. Acer's decline was due to its dependence on the netbook and the direct impact tablets are having on those products.

"IHS believes that the jury is still out on exactly how much tablets are cannibalizing PC sales. However, the rising number of tablet models on the market, along with certain high-profile product launches during the first quarter, caused confusion among consumers as to exactly how to view the tablet platform relative to the PC platform," said Matthew Wilkins, principal analyst for computer platforms.

IHS analysts were surprised at the fall off as the fourth quarter of 2010 represented the best period ever for global PC shipments.

Despite these early month doldrums, IHS expects a turnaround later this year with the global PC marketing growing 8 percent to 373 million units.

HP maintained its top spot with 18.9 percent of the market. Dell continued to hang onto second place with 12.9 percent share. Dell was helped by Acer's 20.4 percent drop. Lenovo and Toshiba filled out the rest of the top five.

IHS iSuppli Figure: Preliminary Top-5 Global Q1 2011 Worldwide PC Shipment Market Share (Share by Shipments in Thousands of Units) Q1 2011 Rank OEM Q1 2011 Shipments Q4 2010 Shipments Sequential Change in Shipments Q1 2010 Shipments Annual Change in Shipments Q1 2011 Market Share 1 Hewlett-Packard        15,374        18,029 -14.7%        15,696 -2.1% 18.9% 2 Dell        10,475        11,296 -7.3%        10,668 -1.8% 12.9% 3 Acer*          9,238        10,091 -8.5%        11,603 -20.4% 11.4% 4 Lenovo          8,100          9,484 -14.6%          7,020 15.4% 10.0% 5 Toshiba          4,695          5,361 -12.4%          4,575 2.6% 5.8%   Others 33,436 38,846 -13.9% 32,034 4.4% 41.1%   Total        81,317        93,107 -12.7%        81,596 -0.3% 100.0%                 *Incorporates founder PC shipments           Source: IHS iSuppli May 2011