Worldwide PC shipments in the first quarter of 2009 fell by the largest historic rate in the seven years iSuppli has been tracking the market, as weaker-than-expected desktop sales dragged down the industry, according to iSuppli.

PC shipments in the first quarter of 2009 amounted to 66.5 million units, an 8.1% decline from 72.3 million units during the same period in 2008, and a 14.4% drop from 77.6 million in the fourth quarter of 2008.

“The worldwide recession sparked by the credit crisis slammed PC shipments for the second quarter in succession during the first three months of 2009,” said Matthew Wilkins, principal analyst for compute platforms research at iSuppli. “The first-quarter performance of the worldwide PC market was worse than iSuppli had expected in its prior forecast, which called for a 4% decline in shipments compared to the same period in 2008. After a long period of immunity to the global downturn, the economic crisis finally has begun to impact the PC market.”

The desktop segment was the major culprit for the PC decline, with first-quarter unit shipments dropping by 23% compared to the same period in 2008. In contrast, notebook shipments grew 10% compared to the first quarter of 2008.

There were no changes in the rankings of the world’s top-five PC vendors in the first quarter compared to the same period a year earlier.

Hewlett-Packard (HP) remained the number one PC vendor for the eleventh successive quarter, with its shipments remaining flat from a year earlier at 13 million units. The company held a market share of 19.7%.

Dell experienced an 18.7% drop in PC unit shipments, declining to 8.8 million units in the first quarter, compared to 10.8 million units during the same period in the 2008. The company’s market share declined to 13.2%, down from 14.9% in the first quarter of 2008.

“Dell’s performance in the first quarter was heavily influenced by its weak desktop shipments, which dragged down its overall market share,” Wilkins said.

The remainders of the top-five were rounded out by the Asian PC vendors, Acer, Lenovo and Toshiba, which had market shares of 11.1%, 6.7%, and 5.2%, respectively.

Toshiba posted the strongest growth among the top-five on a percentage basis, with its shipments rising by 13.5% from a year earlier.

iSuppli in the first quarter continued to observe strong netbook sales through network operator retail stores. The top-five PC vendors cited sales through such outlets as driving demand for their netbook products.

“The bundling of a low-cost portable computer and an Internet access package has clearly struck a chord with consumers,” Wilkins said. “The reduced upfront pricing of such packages provided by monthly contract plans also has been a strong factor propelling their success.” iSuppli predicts netbooks will account for 14% of worldwide notebook PC shipments in 2009, up from 9% in 2008.