Data Structures

The OS is a program, and like any program, it has some key data structures that track various relevant pieces of information. To track the state of each process, for example, the OS likely will keep some kind of process list for all processes that are ready and some additional information to track which process is currently running. The OS must also track, in some way, blocked processes; when an I/O event completes, the OS should make sure to wake the correct process and ready it to run again.

Information of a process that the OS tracks

The snippet below shows what type of information an OS needs to track about each process in the xv6 kernel“The xv6 Operating System” by Russ Cox, Frans Kaashoek, Robert Morris, Nickolai Zeldovich. From: https://github.com/mit-pdos/xv6-public. The coolest real and little OS in the world. Download and play with it to learn more about the details of how operating systems actually work. We have been using an older version (2012-01-30-1-g1c41342) and hence some examples in the book may not match the latest in the source.. Similar process structures exist in “real” operating systems such as Linux, Mac OS X, or Windows; look them up and see how much more complex they are.