The document provides an overview of operating systems, defining them as interfaces between hardware and users that manage resources like memory, CPU time, and disk space. It outlines various types of operating systems, such as Microsoft Windows and Linux, and describes different models like monolithic systems and client-server systems. Key components and tasks of operating systems, including memory management and user interface, are also highlighted.

1. Operating Systems OverviewDesigned for 4th Semester Students of GTU (Gujarat Technical University)

2. What is an Operating SystemAn operating system (OS) is an interface between hardware and user which is responsible for the management and coordination of activities and the sharing of the resources of the computer that acts as a host for computing applications run on the machine.Software that controls the allocation and usage of hardware resources such as memory, CPU time, disk space, and input and output devices.The foundation software of a machine; that which schedules tasks, allocates storage, and presents a default interface to the user between applications.

3. Operating System OverviewUserApplicationOperating SystemHardware

4. Operating System FunctionsIt manages the hardware and software resources of the system. In a desktop computer, these resources include the processor, memory, disk space and many more (On a cell phone, they include the keypad, the screen, the address book,etc).It provides a stable, consistent way for applications to deal with the hardware without having to know all the details of the hardware.

5. Types of Operating Systems

6. Examples of Operating SystemsMicrosoft WindowsMac OS XUnix and Unix-like operating systemsBSD and its descendantsPlan 9Linux and GNUGoogle Chrome OS

7. Concepts/Models of Operating SystemMonolithic SystemsLayered SystemsVirtual MachinesClient Server System

8. Monolithic Operating SystemsThe components of monolithic operating system are organized randomly and any module can call any other module without any reservation. Similar to the other operating systems, applications in monolithic OS are separated from the operating system itself.

9. Layered Operating SystemThe components of layered operating system are organized into modules and layers them one on top of the other. Each module provide a set of functions that other module can call. Interface functions at any particular level can invoke services provided by lower layers but not the other way around.

10. Virtual MachinesVirtual machines are separated into two major categories, based on their use and degree of correspondence to any real machine. A system virtual machine provides a complete system platform which supports the execution of a complete operating system.In contrast, a process virtual machine is designed to run a single program, which means that it supports a single process. An essential characteristic of a virtual machine is that the software running inside is limited to the resources and abstractions provided by the virtual machine—it cannot break out of its virtual world.

11. Client-Server SystemClient–server model of computing is a distributed application structure that partitions tasks or workloads between service providers, called servers, and service requesters, called clients. Often clients and servers communicate over a computer network on separate hardware, but both client and server may reside in the same system. A server machine is a host that is running one or more server programs which share its resources with clients. A client does not share any of its resources, but requests a server's content or service function. Clients therefore initiate communication sessions with servers which await (listen to) incoming requests.

12. Components of Operating SystemsThe user interfaceThe kernelProgram executionInterruptsProtected mode, supervisor mode, and virtual modesMemory managementVirtual memoryMultitaskingDisk access and file systemsDevice driversNetworkingSecurityWe will read details about these components in the next chapters.

13. Operating System TasksThe operating system's tasks, in the most general sense, fall into six categories:Processor managementMemory managementDevice managementStorage managementApplication interfaceUser interfaceWe will read the details about these in the next chapters.

14. Read it again and head for the next chapter