Lecture 1-Part 2: Operating-System Structures

1. Lecture 1-Part 2: Operating-System Structures

2. Operating System Services • Operating systems provide an environment for execution of programs and services to programs and users • One set of operating-system services provides functions that are helpful to the user: • User interface - Almost all operating systems have a user interface (UI). • Program execution - The system must be able to load a program into memory and to run that program, end execution, either normally or abnormally (indicating error) • I/O operations - A running program may require I/O, which may involve a file or an I/O device

3. Operating System Services (Cont.) • One set of operating-system services provides functions that are helpful to the user (Cont.): • File-system manipulation - The file system is of particular interest. Programs need to read and write files and directories, create and delete them, search them, list file Information, permission management. • Communications – Processes may exchange information, on the same computer or between computers over a network • Error detection – OS needs to be constantly aware of possible errors • May occur in the CPU and memory hardware, in I/O devices, in user program • For each type of error, OS should take the appropriate action to ensure correct and consistent computing

4. Operating System Services (Cont.) • Another set of OS functions exists for ensuring the efficient operation of the system itself via resource sharing • Resource allocation - When multiple users or multiple jobs running concurrently, resources must be allocated to each of them • Many types of resources - CPU cycles, main memory, file storage, I/O devices. • Accounting - To keep track of which users use how much and what kinds of computer resources • Protection and security - The owners of information stored in a multiuser or networked computer system may want to control use of that information • Protection involves ensuring that all access to system resources is controlled • Security of the system from outsiders requires user authentication, extends to defending external I/O devices from invalid access attempts

5. A View of Operating System Services

6. User Operating System Interface - CLI Command Line Interface (CLI) or command interpreter allows direct command entry • Sometimes implemented in kernel, sometimes by systems program • Sometimes multiple flavors implemented – shells • Primarily fetches a command from user and executes it • Sometimes commands built-in, sometimes just names of programs • If the latter, adding new features doesn’t require shell modification

7. Bourne Shell Command Interpreter

8. User Operating System Interface - GUI • User-friendly desktop interface • Usually mouse, keyboard, and monitor • Icons represent files, programs, actions, etc • Various mouse buttons over objects in the interface cause various actions (provide information, options, execute function, open directory (known as a folder) • Many systems now include both CLI and GUI interfaces • Microsoft Windows is GUI with CLI “command” shell • Apple Mac OS X is GUI interface • Unix and Linux have CLI with optional GUI interfaces

9. The Mac OS X GUI

10. Touchscreen Interfaces • Touchscreen devices require new interfaces • Mouse not possible or not desired • Virtual keyboard for text entry • Voice commands.

11. User goals and System goals • User goals – operating system should be convenient to use, easy to learn, reliable, safe, and fast • System goals – operating system should be easy to design, implement, and maintain, as well as flexible, reliable, error-free, and efficient

12. The Classification of Operating systems • Multi-user: Allows two or more users to run programs at the same time. Some operating systems permit hundreds or even thousands of concurrent users. • Multiprocessing: Supports running a program on more than one CPU. • Multitasking: Allows more than one program to run concurrently. • Multithreading: Allows different parts of a single program to run concurrently. • Real time: Responds to input instantly.

13. Layered Approach • The operating system is divided into a number of layers (levels), each built on top of lower layers. The bottom layer (layer 0), is the hardware; the highest (layer N) is the user interface. • With modularity, layers are selected such that each uses functions (operations) and services of only lower-level layers

14. Simple Structure -- MS-DOS • DOS (Disk Operating System) gained a reputation by supporting operating systems developed by IBM and Windows. • DOS was prominent in the industry up until support was terminated for Windows ME. • Though it's not as sophisticated as modern systems, DOS offers many advantages to the user. • This system is very stable and rarely endures crashes. • While the system is still used, DOS has become more difficult to manage as support is limited.

15. Non Simple Structure -- UNIX • UNIX is an operating system which was first developed in the 1960s, and has been under constant development ever since. • By operating system, we mean the suite of programs which make the computer work. It is a stable, multi-user, multi-tasking system for servers, desktops and laptops. • UNIX systems also have a graphical user interface (GUI) similar to Microsoft Windows which provides an easy to use environment. • There are many different versions of UNIX, although they share common similarities. • The most popular varieties of UNIX are Sun Solaris, GNU/Linux, and MacOS X.

16. Linux • The Linux operating system is developed on a kernel based on Unix. • It is known as one of the most secure platforms, yet Linux is often viewed as more complex. • Linux is the result of an open-source project, allowing users and developers to access the source code for free. • Because it requires less hardware, Linux is capable of providing exceptional performance even on a smaller hard disk. • Large communities of users exist for this system, constantly contributing to the code and making improvements. • The server-based concept of Linux has resulted in fewer home users .

17. Mac OS X • Mac OS X is Apple's trademark operating system software for their line of Macintosh computers. • The system was based in part on Unix and mimics it's format with the administrative controls. • Mac OS X software requires a low level of maintenance with fewer occurrences of computers worms, viruses and spyware. • The Apple operating system does have some disadvantages, primarily in regard to software and hardware compatibility.

18. Windows • The Microsoft Windows operating system is the most popular choice and currently has a stronghold over the market. • This platform has made significant advancements from version 1.0 all the way to the new Windows 7 system. • The Windows system is highly compatible, feature-rich and has a much larger selection of software applications. • Despite widespread usage, Windows has been heavily associated with the term "insecure" as a number of security vulnerabilities have made it the most targeted system. • Frequently exploited by hackers and malicious code writers, it is recommended that any Windows operating system with internet access be protected by some form of security software.