The proliferation of the desktop computer happened much faster than that, of course, as did the rise of personal computing -- via laptops, PDAs, cell phones and other devices. Personal computing is just one dimension of the epochal movement of computing away from centralized mainframes to client/server computing, multitier distributed computing, grids and more.

But unlike the emergence of the minicomputer and the server, the rise of the PC had special meaning for IT managers: It meant they were no longer in control. That Lotus 1-2-3 spreadsheet user was programming, whether the IT shop liked it or not.

Open-source rides into data centers

The emergence of open-source software predates Linux. Sendmail, originally written in 1983 for Unix, was the first open-source program to be widely adopted by IT departments. Today, it transfers about 70 percent of the Internet's e-mail.

In 1996, the open-source Apache project had become the most popular Web server software on the Internet; by last month, Apache was running more than 80 million sites, for a 62 percent market share. However, with IBM backing Linux, followed by Hewlett-Packard, Oracle and others, Linux has become the face of open-source. Today, the operating system's share of the server market is close to 30 percent.