1.0 Introduction to operating systems 1.1 Operating System Environment

LEARNING OUTCOMES Explain the Operating Systems Environment

1.1.1 Operating System Definition A program that acts as an intermediary between a user of a computer and the computer hardware. Simple word: It is an interface between the user and the hardware. It is the first software that runs when the computer boots up. Its provides a platform for the user to run applications Is a program that manages the computer hardware. Purpose: to provide an environment in which user can execute program in a convenient & efficient manner. Simple word ( primary concept): Providing the system interface. Operating system goals: Execute user programs and make solving user problems easier. Make the computer system convenient to use.

1.1.2 Basic functions of operating system · Managing Resources – These programs coordinate all the computer’s resources including keyboard, mouse, printer, monitor, storage devices and memory. Providing a user interface Running applications Support for built-in utility programs Control to the computer hardware “ Process management, memory management and device management”

Computer System Component COMPONENTS HARDWARE OPERATING SYSTEM APPLICATION PROGRAM USER

Abstract View of Operating System

1.1.3 Operating system structure Monolithic The monolithic operating system is the earliest and most common operating system architecture Every component of the operating system is contained in the kernel and can directly communicate with any other (i.e., simply by using function calls). The kernel typically executes with unrestricted access to the computer system (Fig. 1). Eg : OS/360, VMS Advantage: Direct intercommunication between components makes monolithic operating systems highly efficient. Few calls cross from user space to kernel space Disadvantage: difficult to isolate the source of bugs and other errors particularly susceptible to damage from errant or malicious code.

Fig 1: Monolithic Operating System kernel architecture

2. Microkernel A microkernel operating system architecture provides only a small number of services in an attempt to keep the kernel small and scalable These services typically include low-level memory management, inter-process communication and basic process synchronization to enable processes to cooperate Operating system components outside the kernel can fail without causing the operating system to fall over. the downside is an increased level of inter-module communication which can degrade system performance. Eg: Linux and Windows XP Advantage high degree of modularity, making them extensible, portable and scalable Disadvantage can degrade system performance.

Fig 2: Microkernel Operating system Architecture

3. Layered To overcome the issue of monolithic architecture by grouping components that performs similar functions into layers Each layer communicates with those above and below it. Lower-level layers provide services to higher- level layer using interfaces that hide their implementation Layer OS are more flexible than monolithic OS because the implementation of each layer can be modified without requiring any modification to other layers

Each component hides how it performs its job and presents a standard interface that other components can use to request its services In a layer approach, a user process’s request may need to pass through many layers before it is services Early example of layer OS is THE (Technische Hogeschool Eindhoven) Many of today’s OS including Windows XP and Linux implement some level of layering. Main advantage is simplicity of construction and debugging.

Fig 3: Layers of THE operating system

Networked and Distributed Operating System A network operating system enables its processes to access resources (e.g., files) that reside on other independent computers on a network. The structure of many networked and distributed operating systems is often based on the client/server model A distributed operating system is a single operating system that manages resources on more than one computer system. Distributed systems provide the illusion that multiple computers are a single powerful computer, so that a process can access all of the system’s resources regardless of the process’s location within the distributed system’s network of computers.

Fig 4: Client/server Operating system model

1.1.4 Various architecture of operating systems Single Processor system The system that execute the one process at the time and the next job when process is completed it is called the single process system They have only one main CPU.

Multiprocessor System ( parallel systems) Have more than 1 processor in close communication, sharing the computer bus, the clock, memory and peripheral devices. Advantage Increased throughput. Economy of scale Increased reliability

Clustered System Share storage and are closely linked via LAN Networking. Provide high availability Asymmetric clustering – one machine is in hot standby mode, the other is running the application Symmetric mode – two or more hosts are running application and monitoring each other.

1.1.5 Various Product of Operating System Form a group in two(2). You are require to do some research regarding Operating System Product ( Closed Source System & Open Source System). In your finding identify criteria's of operating system below : Developer / Company Source Model License Official Website Basic Function of Operating System Present your outcomes in power point form for all your friend.

1.1.6 OS concept Multitasking -allow more than one program to run at a time. Multiprogramming -is a rudimentary form of parallel processing in which several programs are run at the same time on a uniprocessor. Time sharing -is the sharing of a computing resource among many users by means of multiprogramming and multi-tasking. -individuals and organizations to use a computer without owning one -schedule tasks for efficient use of the system and may also include accounting for cost allocation of processor time, mass storage, printing, and other resources.

Buffering -is a region of memory used to temporarily hold data while it is being moved from one place to another. Spooling -refers to putting jobs in a buffer, a special area in memory or on a disk where a device can access them when it is ready. Caching is a component that transparently stores data so that future requests for that data can be served faster.

Buffering Spooling allows the I/O of a job to overlap with its own computation allows the I/O of one job to overlap the computation of another CPU overlaps input , output and processing of a single Job CPU Allows overlap of one Job with the computation and output of other job Is an area of main memory for holding data during input and output data transfers Is a buffer that holds output for a device such as printer, that cannot accept interleaved data streams buffering requires an Internet connection. associated with video viewing on the web. Spooling can be carried out online or offline. associated with printing

1.1.7 Component of Operating System Kernel The central module of an operating system. It is the part of the operating system that loads first, and it remains in main memory. in other words it is the heart of the operating system Because it stays in memory, it is important for the kernel to be as small as possible while still providing all the necessary services required by other parts of the operating system and applications Typically, the kernel is responsible for memory management, process and task management, and disk management.

Shell The outermost layer of a program. Shell is another term for user interface. In some systems, the shell is called command interpreter. Operating systems and applications sometimes provide an alternative shell to make interaction with the program easier. For example, if the application is usually command driven, the shell might be a menu-driven system that translates the user's selections into the appropriate commands. UNIX systems offer a choice between several different shells, the most popular being the Cshell, the Bourne shell, and the Korn shell. Each offers a somewhat different command language.

File system is a means to organize data expected to be retained after a program terminates by providing procedures to store, retrieve and update data, as well as manage the available space on the device(s) which contain it. organizes data in an efficient manner and is tuned to the specific characteristics of the device. are used on data storage devices such as hard disk drives, floppy disks, optical discs, or flash memory storage devices to maintain the physical location of the computer files

Directory structure and file naming facilities File system File System File system provide facilities which enable a user to create files, assign meaningful name and specify how the files to be shared with others users of the system File System Directory structure and file naming facilities Protection of file against illegal forms access Static and dynamic sharing of files Reliable storage of files

1.1.8 Interaction between Application and OS An operating system (OS) is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system. A user cannot run an application program on the computer without an operating system, unless the application program is self booting.

1.1.9 Types of Interfaces 1. Command Interface 2. Voice-actuated interface 3. Graphical User Interface 4. Web-form interface

Types of Interface : Command Interface An interface that accepts types commands or special keys on a keyboard to enter data and instruction from the user. Normally is used to configure devices, manage system resources and troubleshoot network connection, network administrators and other advanced users work with a command – line interface. Set command entered into the computer is called the command language.

Types of Interface : Command Interface Difficult to use – they require exact spelling, grammar and the punctuation. Advantages – give a user more control over setting details. Eg: MS-DOS , UNIX operating system

Types of Interface : Voice-Actuated Interface Enables a user to use simple voice command to control physical environmental. Eg: The computer includes a voice card and associated voice recognition and training software for interpreting and translating voice input into digital information readable by controller card for operating equipments or control the environment.

Types of Interface : Graphical User Interface With GUI user interact with menus and visual image such as icon, buttons and other graphical object to issue the command. GUIs evolved from command –driven user interface User often use mouse to point and click on the chosen

Types of Interface : Web-form Interface Allow user to enter data that is send to a server for processing Web form interface resembles paper form because user need to fill out the form using web form elements

Type of OS Interface Command line: Set command entered into the computer Graphical User Interface: driven user interface

Voice Actuated :Enables a user to use simple voice command to control physical environmental Web Form: Allow user to enter data that is send to a server for processing

System calls and application programming interface (api) System call is how a program requests a service from an operating system's kernel. This may include hardware related services (e.g. accessing the hard disk), creating and executing new processes, and communicating with integral kernel services (like scheduling). System calls provide the interface between a process and the operating system. An application programming interface (API) is a source code based specification intended to be used as an interface by software components to communicate with each other. An API may include specifications for routines, data structures, object classes, and variables.

Types of System Calls 􀂄 Process control 􀂄 File management load, execute, end, abort, create, terminate, wait ... memory allocation and deallocation 􀂄 File management open, close, create, delete, read, write, get/set attributes... 􀂄 Device management request / release device, read, write, ... 􀂄 Information maintenance get / set time, date, system data, process / file attributes 􀂄 Communications create / delete connection, send, receive, ...