Why Study Operating Systems?

• Operating Systems (66451) is being offered in Autumn 2023 by Dr. Suleiman Abu Kharmeh.

• The required textbook is "Operating System Concepts, 10th Edition" by Abraham Silberschatz, Peter Galvin, and Greg Gagne.

• An additional textbook is "Operating systems : internals and design principles" by William Stallings.

• "Operating Systems: Three Easy Pieces” by Remzi and Andrea Arpaci-Dusseau is another textbook.

• A free PDF version of "Operating Systems: Three Easy Pieces." is available online.

Why Study Operating Systems?

• To build or modify a real operating system.
• To tune application performance.
• To administer and use a system well.
• Techniques used in an OS can apply to other areas like complex data structures, conflict resolution, concurrency, and resource management.
• To understand the challenge of designing large and complex systems.
• Future decisions regarding operating systems will be based on more secure knowledge.
• To satisfy curiosity about how systems work.

Course Objectives

• To achieve a fundamental understanding of computer operating systems.

• This includes from the moment a PC boots up, to managing devices and memory, up to loading complex, threaded applications.

• To distinguish between the different types of operating systems.

• To identify various OS components and their functions.

• Key topics of analysis include processes and threads, concurrency control, memory management, and file systems.

• Grading is based on a Midterm (30%), HomeWorks/Project (20%), and Final Exam (50%).

Introduction to Operating Systems

• An OS is software between a user program and the hardware.
• The OS manages resources and allocates them.
• The OS is a control program.
• The OS decides between competing requests for hardware access.
• Aims for efficiency and fairness.
• It controls user program execution and prevents errors and improper use.
• Common elements include a GUI, a command line shell, and a text editor, all interfacing with the OS.
• The OS interacts directly with hardware like the mouse, CPU, Memory and keyboard.

OS Fundamentals

• The OS multiplexes resources between applications.

• The OS enforces isolation and protection between applications.

• The OS manages physical resources and expects to have privileged access.

• There are a variety of OSes including, Linux, BSD, and Windows.

• An OS is an interface between applications and hardware.

• It manages resources (CPU, memory, disk accesses) and provides program services.

• The OS mediates program access to hardware resources, covering sharing and protection.

• Manages computation (CPU), storage (memory/disk), network communications (TCP/IP, Ethernet), and I/O devices.

Computer System Layers

• Diagram depicts layers from end-user to computer hardware, including applications, utilities, OS, and hardware.

Operating System Functions

• Tasks include controlling hardware, running applications, managing data/files, and providing user services.
• High-level abstractions (files) replace low-level hardware details for programming and portability (across configurations/architectures).
• User benefits include safety (virtual machines with program protection) and efficiency (resource sharing/concurrent execution).

Operating System Progression

• Linked Library: the OS was a code library linked into programs, offering an API to control resources.

• Resident Monitor (~1950): a continuously running program initialized other programs, managed memory cleanup.

• Timesharing (~1960): allowed multiple terminals to use one machine, dividing CPU time equally.

• Multiprogramming: overlaps I/O of one job with the computing of another, switching between jobs on I/O events.

• Modern OSes: include multi-tasking, parallel processing, mobile OSes, and real-time systems.

Advantages of Multiprogramming

• Increased CPU utilization and throughput.
• Shorter turnaround time particularly for for short jobs.
• Improved memory and resource utilization because they are in higher demand.

Typical Multiprogramming OS

• Windows (Windows 95 through Windows 11).
• UNIX-based systems like Linux, IBM’s AIX, BSD Unix, and macOS.
• Additionally modern mobile OS are UNX based.
• Recent MS-DOS versions support multitasking.
• Modern OSes with multi-core/multi-threading CPUs might be considered parallel operating systems.

Parallel Systems

• Parallel systems are capable of running multiple threads or processes and allow for quicker execution.
• Disadvantages include divides program into multiple parallel activities and OS primitives must include fast communication among activities.
• Advantages are it increase execution speed and simultaneously runs multiple threads/processes on multiple CPUs.
• Common parallel computers comes in 2 forms SMPs (symmetric multi-processors) with few cores and MPPs (massively parallel processors) with thousands of cores.

Mobile Computing

• Mobile OS manages the hardware and enables smartphone/tablet apps.
• It manages multimedia functions, connectivity (internet, touch screen, Bluetooth,GPS navigation, cameras, speech recognition.
• Most mobile OSes such as iOS and Android are Unix based.
• Most OSes aren't interchangeable between devices which means Apple iOS phone have their own Android OS.

Embedded/Pervasive Computing

• Cheep processors make pervasive computing possible.
• Embedded systems often have constrained hardware resources (slow processors, small memory, limited power, no/small disk).
• Usually have one dedicated application and this is all subject to rapid change.

Real-Time Operating Systems (RTOS)

• The RTOS are for highly portable computing devices.
• RTOS are small to save valuable storage and typically dont use much power, and support long battery life.
• They Have fixed/rigid timing requirements.
• Examples include freeRTOS (Amazon), Raspberry Pi OS, µC/OS (Micrium), Embedded Linux.

Distributed/Cloud Based OS

• Distributed systems facilitate the use of geographically distributed resources e.g workstations on a LAN or servers across the Internet.
• They support communications between programs, including inter-process communication (message passing, shared memory) and networking stacks.
• The goal is access to a diversity of resources.
• These systems share distributed resources (hardware, software) e.g load balancing, authentication and access control Speed is not the main focus.

Virtual OS

• Virtual machines solve the problem of application compatibility when upgrading or switching hardware because apps are bound to a particular OS.
• There are many Operating Systems (OSes), Windows and Linux dominate the market.
• It was pioneered by IBM
• Can Run multiple OSes concurrently on the same hardware
• A heavyweight mechanism for maintaining app compatibility.

Terminology

• Virtual Machine Monitors/Manager (VMM) is used
• VMM is software that allows multiple guest OSes to run concurrent on one physical machine and each guest runs on a virtual machine.
• VMM is sometimes called a hypervisor.
• The Host is the original operating system in which the VMM runs.
• Virtual Box or VMWare Player are examples of VMM software.

VMM Organization and Functions

• VMM maps operations on virtual hardware to physical hardware.
• Multiplexes resources between guest OSes.
• Enforces protection and isolation between guest OSes.

Advantages of Virtualization

• Guests are oblivious because of compatibility and functionality.
• It consolidates by running multiple OSes as guests on one machine.
• A guest OS is the only thing at risk.
• Useful for multiple platforms debugging.

Disadvantages of Virtualization

• Performance is lower because the guest operating system compared has to interact with a installed Operating system
• cost/effort of maintenance of multiple operating system.

Summary of Operating Systems

• An OS is software that manages computer hardware & provides a program environment.
• Modern computer architectures are multiprocessor systems where each CPU has multiple computing cores.
• OSes use multiprogramming to let several jobs be in memory at the same time and allow the CPU to always have a job to execute.
• Multitasking is when CPU scheduling algorithms rapidly switch between processes for fast user response.
• Computing also takes place in mobile and cloud computing environments.
• Operating systems can be traditional, client–server, peer-to-peer, and real-time embedded.
• A computer’s hardware can be abstracted into several environments through virtualization.
• GNU/Linux, FreeBSD, and Solaris are examples of open-source systems.
• There are free and open-source operating systems available for use redistribution, and modification.

OS Structures

• The OS mediates access to hardware resources and programs request services via system calls (traps.)Hardware devices request attention via interrupts.
• It sits between the application program and the hardware

User Apps - Operating System Structure

• User Apps (Firefox, Photoshop and Acrobat) use an Operating System
• The Applications use the User Interfaces; GUI/Touch and CLI
• Those User interfaces make System Calls: through Application Programming Interface (API)
• The core Operating systems tasks are, file, memory, and process management
• There network support and device driver functions
• Low level hardware abstraction.

User Interfaces

• What is seen when use the computer are User Interfaces.
• Ease of use is what is determined.
• The command-line, and and graphical user interfaces are the 2 types used.

Command-Line Interfaces (CLI)

• User must type exact commands at a command prompt.
• One advantage is that one must learn the commands, unlike more user friendly interfaces.

Graphical User Interfaces (GUI)

• Easier to use, with menu-based approach so commands did not need to be memorized.
• The breakthrough in ease of use came with the introduction of graphical user interfaces (GUIs).
• The use of a mouse or other pointing device makes this task easier.
• Personal computers today are usually equipped with user friendly GUIs.

System Calls

• System calls provide an interface to OS services and are often written in C and C++.
• Behind the scenes, the functions that make up an API typically invoke the actual system calls.
• An API is a set of functions available to an application programmer.
• Windows API for Windows systems
• POSIX API for POSIX-based systems (which include virtually all versions of UNIX, Linux, and macOS)

System Services/Utilities/Programs

• System Services/Utilities/Programs Provide Program loading, execution and debugging
• Some of the programs are simply user interfaces to system calls
• Consists of file management, a status, Communications, File modification background services and Programming-language support
• A convenient environment for program development and execution.

OS Structure

• The core of an Operating System consists of additional components such as the kernels.
• Can be broken down into, many components, system programs (privileged and non-privileged)
• e.g. bootstrap code, the init program.
• This requires the OS to design a large, complex program that: performs well, is reliable, extensible and backwards compatible.

Towards a Kernel

• The kernel is loaded through the bootloader.
• The "one program running at all times on the computer”
• The architecture of the kernel should be defined by its desired features.

Kernel Features

• Consisting of
• device management, loading and executing programs
• System calls and APIs
• Protection, fault tolerance, and Security e.g. only authorized users should be able to login.
• e.g., programs do not crash the computer

Montiliithic Kernel

• A Montiliithic Kernel consist of a Memory and Process managers.
• CPU Scheduling and security Policies
• System APIs for device access.
• Device access to file systems

Pros/Cons of Monolithic Kernels

• Single code base aids kernel development.
• Robust APIs exist for application developers and no need to find separate device drivers.
• Fast performance is the result of tight coupling.
• Bugs will crash the the entire kernel is and thus, the machine.
• The entire code base is large and is harted to check.
• Device drivers the responsibility of OS developers.
• UNIX/Linux is traditional example of this class of Kernel.

Microkernel

• Micro Kernal is a Kernel limited to Kernel Code and inter-process communication.
• Everything else happens at a user level.

Microkernels

• The goal is to minimize kernel code and organize the OS as user-level processes, increasing isolation, reliability and customization.
• Examples include Mach (CMU), Chorus (French UNIX-like OS), and OS X (Apple) and First release of Windows NT

Pros/Cons of Microkernels

• There is a less code making it easier to check for correctness because micro Kernels are much smaller.
• Making the the entire service more easily configurable.
• Services may crash.
• Performance is often slow

Hybrid Kernel

• A Kernel is used for low level task.
• And other system call request are given to other APIs.

Kernel and their trade offs

• Microkernels is smaller has lower code base and have few features.
• A Hybrid Kernel is a Kernel thats pretty large code base.
• A Montiliithic Kernels have a larger code base and feature list.

Boot Process

• During the boot process the operating systems loads into RAM, from a bootstrap program called a bootloader.

Boot and Recovery Disks

• A boot disk, contains the operating system files needed to boot your computer without accessing the hard disk
• Such disk may contain: installation, trial CD, drivers and user settings
• Bootable USB drive is most common.

Performance Tuning

• Top and ps are unix commands to monitor performance.
• Windows Task Manager provides similar services.
• The goal is to improve performance by removing bottlenecks.