By Katie Marsal

Published: 05:00 PM EST

Growth in Apple's personal computer business continued to outpace the industry average last month, with Macs accounting for a 14 percent unit share and 25 percent dollar share of all US-based PC retail sales, according to market research firm NPD.

The results -- first revealed in an investor note from Pacific Crest Securities analyst Andy Hargreaves on Monday -- represent 60 percent unit growth and 67 percent revenue growth over the same period one year ago. At the same time, overall US PC retail shipments grew just 9 percent on a 5 percent increase in revenues.

Apple saw particular strength in notebook systems, which rose 64 percent in units and 67 percent in revenues, suggesting strong sell-through of the company's new MacBook Air, noted Hargreaves.

"Macbook Air sales appear to be additive to total sales, rather than replacing Macbook Pro sales," he said. "We believe a new set of corporate customers make up a meaningful portion of MacBook Air buyers."

Overall, the US retail segment combined for a 20 percent increase in notebook shipments on an 11 percent rise in revenues.

The Mac maker also saw robust demand for its desktop systems, which grew 55 percent on a 68 percent increase in revenues, compared to the overall retail segment which saw unit sales decline 5 percent on a 2 percent drop in revenues.

"Mac sales do not appear to be negatively impacted by macro environment," Hargreaves concluded. "[The] iMac continues to sell extremely well, with strong sales of larger screen sizes."



Meanwhile, sales of Apple's iPod digital media players remain somewhat limp, and just off their pace from one year ago.

In a separate research note from Piper Jaffray analyst Gene Munster, also issued Monday, it was noted that NPD retail sales data for the month of February suggest total iPod unit sales of 9.5 million to 10.7 million for the three month period ending March.

"Street consensus for March quarter iPods is 10.8 million, representing a 2 percent year-over-year increase; the midpoint of the 9.7m-10.5m range suggests a 4 percent year-over-year decline," Munster wrote. "We see this data point as a slight positive, given this range is a slight increase from what NPD data indicated after 1 month of data."

Both Hargreaves and Munster remain bullish on shares of the Cupertino-based Apple, with Hargreaves noting that the company's current valuation is particularly attractive with the stock trading at just 18 times fiscal year 2008 free cash flow.