What is an operating system?

"The operating system manages the resources of the computing environment by providing a hierarchical file system, process management, and other housekeeping functions [so that the user is not burdened with these tasks]."
-- "The UNIX System", S. R. Bourne, 1983

"The operating system manages the resources of the computing environment by providing a hierarchical file system, process management, and other housekeeping functions [so that the user is not burdened with these tasks]."