by , 6:25 PM EDT, October 17th, 2005

Apple Computer's market share of the U.S. computer market climbed to 4.3% in the September quarter, according to market research firm IDC. That's an increase from 3.3% from the year-ago quarter. Apple was the number five vendor in the U.S. market, behind Dell, HP, Gateway, and Lenova (formerly IBM's PC division), and the company showed a steeper climb in U.S. unit sales, 44.6%, than any other company in IDC's report.

IDC broke Apple's U.S. unit sales at 737,000 units. By comparison, number one vendor Dell shipped some 5.638 million PCs in the US. Dell had 33.2% of the market, well ahead of perennial number two HP, which had 20.3% of the market.

Gateway, a company that worked hard to be allowed to license the Mac OS in the early 1990s, showed what IDC called the second consecutive quarter of significant recovery. In recent years, the company had been seen as being on hard times with declining fortunes. In the September quarter, Gateway was the number three U.S. vendor. The company posted a 35.2% growth in unit sales, second to Apple, and claimed some 6.4% market share.

Worldwide, Apple saw a 48% increase in unit sales, but didn't crack the top five PC vendors (Dell, HP, Lenova, Acer, Siemens). IDC didn't specify Apple's worldwide market share, but extrapolating from Apple's own total Mac unit sales of 1.236 million Macs, a record quarter for the company, the company had some 2.3% global market share.

Such extrapolations are dangerous, at best, because IDC does not rely solely on corporate numbers, but uses its own formulas and research methods to determine units shipped. Using Apple's reported unit sales to determine market share based on IDC's global numbers is therefore an inexact science. Nonetheless, this rough and ready estimate shows Apple is holding its own in the global market.

Total worldwide unit sales increased by 17%, and IDC noted that this was despite increasing energy prices and interest rates. It was the low end of the market, a market Apple addressed earlier in 2005 with the inexpensive Mac mini, that drove overall growth. U.S. total shipments grew by 11%.

[Update: This story was updated with additional information and details. - Editor]