Editor's Note: Reprinted with permission from "After The Software Wars," a new book in which former Microsoft employee Keith Curtis explores the intersection between the worlds of proprietary and free software. The full book is available for purchase and download.

I first met Bill Gates at the age of twenty. He stood in the yard of his Washington lakefront home, Diet Coke in hand, a tastefully small ketchup stain on his shirt, which no one had the courage to point out, and answered our questions, in-turn, like a savant. As a college summer intern, I had planned for a potential encounter and I approached him with questions that interested me but which would be arcane to non-computer mortals.

His answers demonstrated that he was one of the top software experts on the planet and convinced me that I would be very wise to start off my career at Microsoft.

I joined Microsoft in 1993 when it was hitting its stride. It had recently released Windows 3.1 and Windows NT, setting itself on the path of more than a decade of dominance in the PC operating system market, and the many other markets that flow from it. I worked as a programmer for 11 years in various different groups — on databases, Windows, Office, MSN, mobility, and research.

One day it just hit me — I should quit.

Keith Curtis

There were no big reasons, only a lot of little ones. I had just launched v1 of the client and server side of the Microsoft Spot watch, and while it contained sophisticated technologies, I didn’t really believe it would take off in the marketplace. I had gained lots of knowledge yet only understood the Microsoft world. I was making decent money, but had no time to enjoy it. Though my boss was happy with me, I was losing motivation to just keep doing the same thing I had been doing for over a decade. When I looked around the company I saw a lot of ancient codebases and unprofitable ventures.

Like many of my fellow employees, I was only vaguely familiar with free software when I left and decided to try Linux on a lark. At Microsoft, I got all the software I wanted for free, and I always thought free software would be behind proprietary software. For 15 years I had made it a priority to learn about many aspects of Microsoft technologies, and my office contained rows of books on everything from Undocumented Windows to Inside SQL Server. When running Windows I felt as comfortable as Neo in the Matrix, without the bullets and leather, so while I was willing to look around, I was half-forcing myself and didn't want this little experiment to mess up my main computing environment.

Every technical decision was big for me: which version of Linux should I try? Should I get an extra machine or can I try this dual-boot thing? Can I really trust it to live on the same hard drive as Windows? I got some tips and assurance from a Microsoft employee who had already tried Linux, and with that, and the help of Google, I proceeded with the installation of Red Hat's Fedora Core 3.

While I came to not be all that thrilled with Fedora itself, I was floored merely by the installation process. It contained a graphical installer that ran all the way to completion, it resized my NTFS partition — which I considered a minor miracle, setup dual boot, and actually did boot, and let me surf the Web. I didn’t have a clue what to do next, but the mere fact that this all worked told me more about the potential of Linux than anything I had read so far. You cannot, by accident, build an airplane that actually flies.

However, as I dug deeper, I also started to realize that while Linux had a tremendous amount of potential and is doing well on the server and other specialized scenarios, it was not on a trajectory to take over the desktop, which is the most important use of computers, and this book will discuss its remaining challenges.

The Linux Kernel

The kernel of an operating system (OS) is the central nervous system of a computer. It is the first piece of software that the computer executes, and it manages and mediates access to the hardware. Every piece of hardware needs a corresponding kernel device driver, and you need all of your drivers working before you can run any of your software. The kernel is the center of gravity of a software community, and the battle between free software and Windows is at its lowest level a battle between the Linux and Windows kernels. Microsoft has said that it has bet the company on Windows, and this is not an understatement! If the Windows kernel loses to Linux, then Microsoft is also lost.

The Linux kernel is not popular on desktops yet, but it is widely used on servers and embedded devices because it supports thousands of devices and is reliable, clean, and fast. Those qualities are even more impressive when you consider its size: printing out the Linux kernel's 8,000,000 lines of code would create a stack of paper 30 feet tall! The Linux kernel represents 4,000 man-years of engineering and 80 different companies, and 3,000 programmers have contributed to Linux over just the last couple of years.

That 30-foot stack of code is just the basic kernel. If you include a media player, web browser, word processor, etc., the amount of free software on a computer running Linux might be 10 times the kernel, requiring 40,000 man-years and a printout as tall as a 30-story building.

This 40 man-millennia even ignores the work of users reporting bugs, writing documentation, creating artwork, translating strings, and other non-coding tasks. The resulting Linux-based free software stack is an effort that is comparable in complexity to the Space Shuttle. We can argue about whether there are any motivations to write free software, but we can't argue that it's already out there — so there must be some!

One of the primary reasons I joined Microsoft was I believed their Windows NT (New Technology) kernel, which is still alive in Windows Vista today, was going to dominate the brains of computers, and eventually even robots. One of Bill Gates' greatest coups was recognizing that the original Microsoft DOS kernel, the source of most of its profits, and which became the Windows 9x kernel, was not a noteworthy engineering effort. In 1988, Gates recruited David Cutler from Digital Equipment Corporation, a veteran of ten operating systems, to design the product and lead the team to build the Windows NT kernel, that was released as I joined in 1993.

Windows has become somewhat popular for servers and devices, but it never achieved the dominance it did on desktop PCs. Perhaps the biggest reason is that its code wasn't available for others to extend and improve upon. The Linux kernel took off because there is a huge number of people all over the world, from Sony to Cray, who tweaked it to get it to run on their hardware. If Windows NT had been free from the beginning, there would have been no reason to create Linux.

However, now that there is the free and powerful Linux kernel, there is no longer any reason but inertia to use a proprietary kernel.

Excerpted from "After the Software Wars," by Keith Curtis.