MULTIMEDIA TECHNOLOGY SMM 3001 OPERATING SYSTEM

how operating systems software manage the computer how operating systems software manage the computer the basic anatomy of a single- user OS the basic anatomy of a single- user OS the added ingredients for supporting a multi-user OS the added ingredients for supporting a multi-user OS the basic features of graphic user interfaces the basic features of graphic user interfaces In this Chapter…

n an OS is a collection of resident programs that manage the system’s resources manage the system’s resources supervise the execution of processes supervise the execution of processes provide useful services and security provide useful services and security Operating System

Operating system The role of OS has 2 advantages : The role of OS has 2 advantages : Relieves the users from handling the myriad of details necessary for the managing the system Relieves the users from handling the myriad of details necessary for the managing the system Create powerful services that provide abstract view of the computer’s capabilities Create powerful services that provide abstract view of the computer’s capabilities

Managing the system Application programs can exploit the services of the OS Application programs can exploit the services of the OS A system call is a particular request to the OS to perform needed service A system call is a particular request to the OS to perform needed service Eg. Finding a file, allocating memory, etc Eg. Finding a file, allocating memory, etc Without this assistance, application programs would have more complicated tasks to perform Without this assistance, application programs would have more complicated tasks to perform

Managing the system (con’t) OS also protects the computer system from errors committed by users or processors OS also protects the computer system from errors committed by users or processors OS interrupt processes if program commits an illegal condition called exception OS interrupt processes if program commits an illegal condition called exception OS also prevents users from performing action that might have undesirable results OS also prevents users from performing action that might have undesirable results

n Single-user/single programming OS – afford only execution of one process a time by one user at a time n Single-user OS are usually designed into functional units; each unit has a specific set of responsibilities Anatomy of the Single-User OS

Anatomy of the Single-User OS (con’t) n A typical single-user system has the following functional units : n Supervisor n I/O control drivers n Memory Manager n File Manager n User Interface

Anatomy of the Single-User OS (con’t) n SUPERVISOR–oversee and control the execution of processes n The supervisor manages special requests for services made both by users and user processes n The supervisor accepts the request and oversees the loading & execution of the OS program that actually does the work

SUPERVISOR System calls from applications User commands and applications CPU

Anatomy of the Single-User OS (con’t) n I/O CONTROLLER–service routines that standardize I/O operations for users and processes n Eg. To access information stored on a magnetic hard disk, it’s necessary to do the following : n Seek the track n Identify the sector n Read/write the data track n I/O service routine simply transferring & storing data on the system

n MEMORY MANAGER–allocates memory segments for system and user processes Anatomy of the Single-User OS

n FILE MANAGER–creates and manages the file system for storing user’s data n Data is organised in entities called files n A file is a sequence of items treated as a single unit & identified by the system with a unique name n File manager creates & maintains the set of files stored on a specific system n Most of the OS offers a hierarchical file structure (HFS) n Levels such as directories/folders are maintained Anatomy of the Single-User OS

n USER INTERFACE–medium for user communication Text-based Command Line Interpreters (CLIs) Text-based Command Line Interpreters (CLIs) terse, powerful terse, powerful steeper learning curves, unforgiving steeper learning curves, unforgiving Graphical User Interfaces (GUIs) Graphical User Interfaces (GUIs) intuitive, user-friendly intuitive, user-friendly slower, less efficient slower, less efficient Anatomy of a Single-User OS

n multi-user computer systems service a group of users simultaneously n multi-user systems are usually based on uniprocessor hardware n the OS supports multiple users by multiprogramming (multiprocessing) executing multiple processes during a given period of time executing multiple processes during a given period of time Anatomy of a Multi-User OS

Multiprogramming

n Multi-programming means that the system can execute several processes during a given period of time n Multiuser OS are usually based on serial processors n Processor switch back & forth from one program to another Anatomy of a Multi-User OS

Processors not that smart to manage & juggling of required programs Processors not that smart to manage & juggling of required programs A multiuser enable the system is managed more efficiently compared to single user OS A multiuser enable the system is managed more efficiently compared to single user OS To support multiprogramming & multiple users, functions additional to single user OS To support multiprogramming & multiple users, functions additional to single user OS Context switching by supervisor Context switching by supervisor CPU scheduler CPU scheduler Virtual memory by memory manager Virtual memory by memory manager Anatomy of a Multi-User OS

SUPERVISOR – handles the details of changing between processes SUPERVISOR – handles the details of changing between processes supports context switching between ready processes supports context switching between ready processes “context switching”–the OS interrupts the current process; stores information for resuming that process; loads and commences the next ready (waiting) process “context switching”–the OS interrupts the current process; stores information for resuming that process; loads and commences the next ready (waiting) process Anatomy of a Multi-User OS – Context switching

n CPU SCHEDULER–determines the order for ready and waiting processes n The scheduler maintains a list of waiting processes that are ready for execution n The round robin method is used to ensure all waiting processed are treated fairly Anatomy of a Multi-User OS

example: ROUND ROBIN example: ROUND ROBIN

n MEMORY MANAGER–creates the illusion of a larger memory space (virtual memory) n Most multiuser systems often lack of main memory for processing n RAM is not enough for OS, executing processes and data n OS establishes memory address space that is larger than physical main memory Anatomy of a Multi-User OS

Additional space is borrowed from system’s hard drive Additional space is borrowed from system’s hard drive OS maintains virtual address’s space by shuttling data back & forth between secondary memory & primary memory OS maintains virtual address’s space by shuttling data back & forth between secondary memory & primary memory

Human-Computer Interaction: Text Based Interfaces User interface – medium through user communicate to the OS User interface – medium through user communicate to the OS User expresses commands as a series of short text strings typed at the keyboard User expresses commands as a series of short text strings typed at the keyboard

Graphical User Interfaces Employs visual elements on the display monitor such as icons, windows Employs visual elements on the display monitor such as icons, windows GUIs are more intuitive, easy to use, more friendly & helpful environments GUIs are more intuitive, easy to use, more friendly & helpful environments Icons – small pictures depicting devices, files, programs etc Icons – small pictures depicting devices, files, programs etc Windows – rectangular frames that displayed documents & icons Windows – rectangular frames that displayed documents & icons Pointer – use to manipulate icons & windows Pointer – use to manipulate icons & windows

icon

Menus & Dialog boxes Most GUIs support several types of menus : pull down, pop- up, contextual & submenus Most GUIs support several types of menus : pull down, pop- up, contextual & submenus