Apple’s iPad isn’t just affecting the tablet market, it’s having an effect on the overall PC market too.

[ad#Google Adsense 300×250 in story]According to market research firm Gartner, worldwide PC shipments were 84.3 million units in the first quarter of 2011, a 1.1 percent decline from the first quarter of 2010. The reason, or at least a big part of it, is Apple’s iPad.

“With the launch of the iPad 2 in February, more consumers either switched to buying an alternative device, or simply held back from buying PCs,” said Mikako Kitagawa, principal analyst at Gartner. “We’re investigating whether this trend is likely to have a long-term effect on the PC market.”

Gartner had forecast a 3 percent growth for the first quarter, which was off about 4 percent.

In the U.S., PC shipments totaled 16.1 million units in the first quarter of 2011, a 6.1 percent decline from the first quarter of 2010. Kitagawa said it was tablets that affected those numbers too.