Terry A. Davis and building a world of his own.

Terry A. Davis was an American programmer who created an operating system called TempleOS. What makes it unusual is that he spent years building most of it himself, from the kernel to its programming language.

Building an operating system is a long project in itself. There is memory management, the screen, keyboard, files and much more to work on. Terry went further and built a programming language, compiler and various tools for TempleOS too.

What was TempleOS like?

The first thing you might notice about TempleOS is how it looks. Its interface runs at 640×480 and uses 16 colors. The look brings older computers to mind and is one of the system’s distinctive choices.

The system was developed for 64-bit x86 processors. It did not focus on features we now take for granted, such as an internet connection. It was a self-contained environment designed along with its own tools and applications.

HolyC

HolyC, the language used by TempleOS, was inspired by C. You can write and run code within the system itself. One of the most striking things about the project is that Terry developed the language and compiler alongside the operating system.

// A simple HolyC example
U0 Hello()
{
  "Hello, TempleOS!\n";
}

Applications and the kernel run at the same privilege level in TempleOS. This makes the system simpler, but it also means an error in a program can affect the whole system. It is a very different approach from that of a modern operating system designed for everyday use.

Terry A. Davis

Terry lived with schizophrenia. He believed God had told him to develop an operating system, and that belief became part of TempleOS’s design. He faced serious difficulties in the final years of his life.

He died in 2018, leaving behind an operating system whose source code can be explored and which can still be run in a virtual machine. Looking at TempleOS, you can see the work one person put into it over many years.