Chapter 3 Operating Systems Introduction to CS 1 st Semester, 2015 Sanghyun Park

Outline  History of Operating Systems  Operating System Architecture  Coordinating the Machine’s Activities  Handling Competition Among Processes(skipped)  Security(skipped)

History of Operating Systems  An Operating System (OS) controls and coordinates usage of a machine’s __________ (CPU, memory, disks, …)  Single-processor machines in 1940s and 1950s  Significant preparation of mechanical equipment to run a program  Execution of a program → ____  Separation of users and equipments (introduction of computer operator concept)  Submit program to operator to run, along with any required ____ and special _________  Operator _____ program materials into machine’s mass storage  Batch processing – the execution of jobs by collecting them in a single _____, then executing them _______ further _________ with the user

Batch Processing  ___ interaction with the program once submitted

Interactive Processing  What happens when we have multiple users?  Time-_______ solution (time slices)  In single-user systems usually called ___________

Software Classification  Application: spreadsheets, games, program development software  Utility: utility to format a disk, copy a file, utility to handle network communication  Operating system

Operating System Components  Shell: ________ between users and operating systems  Modern computers have a _____ shell  Window manager: component within the GUI shell  Kernel: ______ part of an OS

OS Kernel Software Components  File manager  Coordinates use of machine’s mass _______  Device drivers  Controls operation of machine’s ________ devices (printer, monitor, …)  Memory manager  Coordinates machine’s use of main ________  Scheduler  Determines which ________ is executed ______  Dispatcher  Controls allocation of _____ slices to activities

Boot Strapping in OS

File Manager  Keep ________ of files stored in secondary storage  _________ of each file  Which users are allowed to access which files  _________ space in secondary storage  Group files into a bundle called a __________ or folder  A directory may contain other directories called ____________  A chain of directories within directories is called a directory _____  Provide means to access files (open and manipulate files)

Memory Manager  Charged with the task of coordinating the machine’s use of main memory  Such duties are minimal in ‘one task at a ____’ environment  The program for the current task is placed in main memory, executed, and then replaced by the program for the next task  The duties are extensive in _________ or multitasking environment  Many programs and blocks of data reside in main memory concurrently  Allocate areas of memory for each program  Fulfill memory requirements for programs  Keep track of memory areas no longer occupied

Virtual Memory  When total main memory required _______ actually available?  Memory manager creates _______ of additional memory space by ________ programs and data back and forth between main memory and secondary storage  Illusionary memory space is called _______ memory  Memory requirements are allocated in units called ______ (page size < 4KB)  When a main memory of 256MB is required, but only 128MB is actually available?  Memory manager _______ contents of pages in secondary storage  When a page in secondary storage is needed for access, _____ it in main memory  If no space in main memory, _____ some other page no longer required to secondary storage

Concept of a Process  Distinction between a program and the activity of executing a program  Program  static set of directions  Activity of executing a program  dynamic activity  known as a ________  Process state  Current ________ in the program being executed (value of PC)  _______ in other registers and associated memory cells  A single program can be associated with ___________ one process  In a time-sharing computer, processes _________ for time slices  It is the task of operating system to coordinate these processes

Process Administration (1/2)  The tasks associated with process coordination are handled by the _________ and _________ within OS kernel  Scheduler  Maintains a block of information in main memory called _____________  When a new task is assigned to machine, creates a process for that task by placing a new _____ in the process table  Memory area assigned to process (from memory manager)  Process priority  Process status (ready, waiting for some event (I/O for example))  Determines which activity is executed first  Dispatcher  Ensures that the scheduled processes are actually executed  Divides time into time slices (quantum)  Process __________

Process Administration (2/2) At interrupt  CPU completes current machine _____, _______ current process state, and transfers control to an _________ handler  Interrupt handler is part of dispatcher Dispatcher  Selects a _____ process from the process table (highest priority)  _______ time circuit for the next interrupt  Allow selected process to ______ execution Sometimes, the process time slice is terminated ______ the timer expires (for example when executing I/O)