Retail book sales indicate the market for computer books has experienced a steady decline since the middle of 2008, with subjects related to Mac and iPhone development showing solid growth amid an otherwise morose outlook.

A report on the computer book market, published by O’Reilly’s Mike Hendrickson and based on Nielsen Bookscan retail sales data, reflects the overall status of the computer industry itself and the economy in general. Hendrickson described the report as “lots of bad news peppered with small glimmers of hope.”

Within the top 121 categories of computer books, the report cited only 8 subject areas that could claim a year over year increase in sales during the first six months of 2009.

Within that short list of recession-defying growth was Mac programming, Objective C, online video, mobile programming, and open source topics, providing additional evidence of the significant shift in interest toward iPhone development. While none of those growth categories could claim a place within the top twenty in terms of units sold, the historically popular subjects all experienced major declines.

The data showed that books related to ‘Windows consumer’ experienced the greatest decline year over year. Sales of books on the Mac OS also fell significantly, although the market for Mac-releated books is and continues to be significantly greater than half as large as the market for Windows books, a sharp discrepancy from published market share figures of actual PC sales, where Macs account for less than ten percent of US sales.