An operating system (OS) is the software responsible for controlling and managing hardware and basic system operations, as well as running application software such as word processing programs, Web browsers, and many others. In general, the operating system is the first layer of software loaded into memory when a computer starts up. All other software that gets loaded after it depends on the operating system to provide various common core services, such as disk access, memory management, process scheduling, and user interfaces.
Building Operating Systems is much about studying existing systems, knowing common problems, knowing what other people did, and figuring out if their ideas can be applied to a given new problem. These long-lasting principles - as opposed to implementation details and user interfaces of today's systems/software - is what this lecture is about.