What is an Operating System p opend ing Systems g It is an extended machine top-down view H Hides the messy details which must be performed H Presents user with a virtual machine. easier to use g It is a resource manager bottom-up view m Each program gets time with the resource e.g. Multiple programs run on one CPU H Each program gets space on the resource e.g. main memory is divided up among several running programs Gao Haichang, Software School, Xidian UniversityOperating Systems Gao Haichang , Software School, Xidian University 8 What is an Operating System?  It is an extended machine top-down view  Hides the messy details which must be performed.  Presents user with a virtual machine, easier to use.  It is a resource manager bottom-up view  Each program gets time with the resource e.g. Multiple programs run on one CPU.  Each program gets space on the resource e.g. Main memory is divided up among several running programs