In this fourth post (posts one, two and three are found here) on the State of the Computer Book Market, we will look at programming languages and drill in a little on each language area.

Overall, the market for programming languages was down -6.27% in 2010 when compared with 2009. There were 6,303,125 units sold in 2009 versus 5,931,452 units sold in 2010, which is a decrease of -371,673 units. Java experienced the biggest gain in units, at 28,633 more units in 2010 than 2009, while PHP occupied the opposite end with the biggest decrease at 38,614 fewer units year-over-year.

Before we begin to drill in on the languages, we thought it would be best to explain our "language dimension." When we group books by their language dimension, we categorize them by the language used in …

In this second installment (the first post can be found here), we look at computer book sales in specific technology categories. Remember that we've organized the data into six "Category Families" — Systems and Programming, Web Design and Development, Business Applications, Digital Media Applications, Consumer Operating Systems and Devices, and Computer Topics. Within each of these Families are category group, super-category, category, and atomic category, in a five-level hierarchy. For example, Systems and Programming includes the category groups programming languages, databases, software engineering, general programming, security, and so on. In the rest of this post, we will contrast the final quarter of 2010 with 2009 as well as the whole year of 2009 with 2010.

As a refresher, here is a new treemap of the Category Families, with their sub-areas for the final quarters of 2010 compared …