THE STUDY OF OPERATING SYSTEMS

 There has never been a more interesting time to study operating systems, and it has never been easier. The open-source movement has overtaken operating system, causing many of them to be made available in both source and binary (executable) format. The list of operating systems available in both formats includes Linux. BSD UNIX, Solaris, and part of macOS. The availability of source code allows us to study operating systems from the inside out. Questions that we could once answer only by looking at documentation or the behavior of an operating system we can now answer by examining the code itself.

Operating systems that are no longer commerically viable have been open-souced as well, enabling us to study how systems operated in a time of fewer CPU, memory, and storage resources. An extensive but incomplete list of open-soiurce operating-system projects is available from http://dmoz.org/Computers/Software/Operating.Systems/Oepn.Sources/. computer function makes it possible to run many operating systems on top of one core system. For example, VMware (http://www.virtualbox.com) provides a free, open-source virtual machine manager on many operating systems. Using such tools, students can try out hundreds of operating systems without dedicated hardware.

In some cases, simulators of specific hardware are also available, allowing the operating system to run on "native" hardware, all within the confines of a modern computer and modern operating system. For example, a DECSYSTEM-20 simulator running ono macOS can boot TOPS-20, load the source topes, and modify and comile a new TOPS-20 kernel. An interested student can search the Internet to find the original papers that describe the operating system, as well as the original manuals.

The advent of open-source operating systems has also made it easier to make the move from student to operating-system distribution. Not so many years ago, it was difficult or impossible to get access to source code. Now, such access is limited only by how much interest, time, and disk space a student has.