Operating Systems: Von Neumann Architecture

• Operating Systems are basis on operating systems
• Computer system: monitor, external speaker, keyboard, mouse, computer tower, floppy drive, CD/DVD-ROM drive, hard drive, RAM chips, expansion slots, video card, network card, A/V card, internal speaker, battery, Microprocessor, cooling blades, clock, motherboard, cooling fan

Von Neumann Architecture

• Includes PC, Registers, and ALU which make up the CPU
• Also contains Memory and Interfaccia di I/O (Interface)
• Contains BUS which controls dati (data), indirizzi (addresses), and controllo (control)

Computer System Structure

• Divided into four components: users, application programs, operating system, and hardware
• Users include people, machines, and other computers needing computing resources
• Application programs define how system resources solve user problems
• Word processors, web browsers, database systems, and video games are examples of application programs
• Operating systems control and coordinate use of hardware among various applications and users
• Hardware provides basic computing resources like CPU, memory, and I/O devices

What is an Operating System?

• A program acting as an intermediary between a computer user and the hardware
• Goals include executing user programs, making problem-solving easier, being convenient, and using hardware efficiently

What Operating Systems Do

• Dependent on point of view
• Users desire convenience, ease of use, and good performance, not caring about resource utilization
• Mainframes and minicomputers must keep all users happy, acting as resource allocators and control programs
• Operating systems ensure efficient hardware usage and manage program execution
• Dedicated systems like workstations use dedicated but also shared resources from servers
• Mobile devices optimize usability and battery life with mobile user interfaces like touch screens and voice recognition
• Embedded computers in devices and automobiles lack user interfaces, running without intervention

Defining Operating Systems

• The term covers many roles and has myriad designs/uses
• Operating systems are found in toasters, ships, spacecraft, game machines, TVs, and industrial control systems
• The need for resource management and program control arose when fixed-use military computers became more general-purpose

Different Operating Systems

• MacOS: A series of GUI operation systems developed by Apple Inc. for their Macintosh computers
• Linux: A Unix-like computer operating system assembled under a model of free and open-source software development and distribution
• Microsoft Windows: A series of GUI operating systems developed, marketed, and sold by Microsoft
• iOS: A mobile operating system developed and distributed by Apple Inc. originally unveiled in 2007 for the iPhone, extends to support other Apple devices such as the iPod Touch
• Android: A Linux-based OS designed primarily for touchscreen mobile devices such as smartphones and tablet computers, initially developed by Android Inc.
• BSD/OS: Had a reputation for reliability in server roles. W. Richard Stevens used it for his personal web server

Evolution of Operating Systems

• Serial Processing → Batch Processing → Multiprogramming → Time Sharing → Parallel System → Network-Based → Distributed System

Operating System Definition:

• An Operating System is a set of basic programs and utilities running on a computer
• The kernel, which is part of the operating system, is the one program running on the computer at all times
• A system program ships with the operating system but is not part of the kernel
• An application program is not associated with the operating system
• Modern operating systems include middleware to provide additional services to application developers

Computer System Organization

• CPUs and device controllers connect via a common bus to access shared memory
• Memory stores both data and instructions
• CPUs and devices execute concurrently and compete for memory cycles

Computer-System Operation

• I/O devices and CPUs can run at the same time
• Device controllers manage particular device types with a local buffer
• Operating system device drivers manage each device controller type
• CPUs move data to / from main memory to / from local buffers
• I/O moves from the device to the local buffer of the controller
• Device controllers inform the CPU of operation completion through an interrupt

Common Functions of Interrupts

• Interrupts generally transfer control to an interrupt service routine via the interrupt vector
• The interrupt vector contains the addresses of all service routines
• Interrupt architecture must save the address of the interrupted instruction
• A trap, or exception, is a software-generated interrupt from an error or user request
• Operating systems are interrupt-driven

Storage Structure

• Main memory is the only large storage medium accessible by the CPU
• This memory allows random access but is typically volatile
• Typically random-access memory in the form of Dynamic Random-access Memory (DRAM)
• Secondary storage, like hard drives, provides large, nonvolatile storage capacity

Storage Structure (Cont.)

• Hard Disk Drives (HDD) consist of rigid metal or glass platters with magnetic recording material
• Divided into logic tracks, and subdivided into sectors
• Disk controllers determine the logical interaction between devices and computers
• Non-Volatile Memory (NVM) devices are faster and nonvolatile
• Uses various technologies and becoming more popular as capacity/performance increases and prices drop

Storage Definitions and Notation Review

• Bit: The basic unit of computer storage that contains one of two values(0 and 1)
• Byte: Is 8 bits and an easy chunk of storage for computers.
• Word: A given computer architecture's native unit of data
• Kilobyte (KB): 1,024 bytes
• Megabyte (MB): 1,024^2
• Gigabyte (GB): 1,024^3
• Terabyte (TB): 1,024^4
• Petabyte (PB): 1,024^5

Storage Hierarchy

• Storage systems are organized in a hierarchy based on: Speed, Cost, Volatility
• Caching copies information into a faster storage system
• Main memory acts as a cache for secondary storage
• Device Drivers provide a uniform interface between the controller and the kernel to manage I/O

Storage-Device Hierarchy

• Top to bottom: Registers, Cache, Main Memory, Nonvolatile memory, Hard-disk drives, optical disk, Magnetic tapes, with access time slowing down and storage capacity growing larger

Computer System Architecture

• Most systems use a single general-purpose processor, and may also have special-purpose processors
• Multiprocessor systems grow in use and importance
• These are known as parallel systems or tightly-coupled systems

Computer-System Architecture Advantages

• Increased Throughput
• Economy if scale
• Increased Reliability- graceful degradation or fault tolerance

Two Types of systems

• Asymmetric Multiprocessing: each processing assigned a specific task
• Symmetric Multiprocessing- each processor performs all tasks

Symmetric Multiprocessing Architecture

• Multiple processors (processor0, processor1)
• Each processor has a CPU
• Each CPU has registers and cache
• All processors access a main memory block

Dual-Core Design

• Features multi-chip and multicore
• Systems containing all chips, with chassis containing multiple separate systems
• Each processor has a CPU core
• Each core has registers and an L1 cache
• Each processor shares an L2 cache

Non-Uniform Memory Access System

• memory0 and memory1, CPU0 and CPU1, CPU 2 and memory2, and CPU3 and memory3- all interconnect via interconnect

Clustered Systems

• Like multiprocessor systems, but multiple systems work together
• Usually sharing storage via a storage-area network (SAN)
• Provides a high-availability service which survives failures
  • Asymmetric clustering has one machine in hot-standby mode
  • Symmetric clustering has multiple nodes running applications, monitoring each other
• Some clusters are for high-performance computing (HPC)
• Applications must be written to use parallelization
• Some have distributed lock manager (DLM) to avoid conflicting operations

Clustered Systems Architecture

• A number of computers (e.g. 3) are interconnected via a small network interconnect
  • Each is connected to the storage-area network

PC Motherboard

• Has DRAM slots for RAM, processor socket (for CPU), Peripheral Component Interconnect (PCI) bus slots, and I/O and power connectors
• Processor socket contains CPU, DRAM is RAM, PCIe is for graphics card
• Motherboards in advanced computers allow more than one system board

Computer Startup

• A bootstrap program is loaded at power-up or reboot
• Typically stored in ROM or EPROM, generally known as firmware
• Initializes all aspects of system
• Loads operating system kernel in the RAM and starts execution

How a Modern Computer Works

• Thread execution caches for data movement
• CPUs request data to devices at (*N) speed
• Devices have data interrupt (*M) speed
• Von Neumann architecture

Direct Memory Access Structure

• Used for high-speed I/O devices able to transmit information at close to memory speeds
• Device controller transfers blocks of data from buffer storage directly to main memory without CPU intervention.
• Only one interrupt is generated per block, rather than the one interrupt per byte

Multiprogramming (Batch system)

• Single user cannot always keep CPU and I/O devices busy
• With multiprogramming, the code and data are so that has one to execute so the CPU is always busy
• A subset of total jobs in system is kept in memory
• A job is selected and run via job scheduling
• When job has to wait, OS switches to another job

Multitasking (Timesharing)

• A logical extension of batch systems, the CPU switches jobs frequently so that users can interact with each job while it is running, creating interactive computing
• Response time should be less than 1 second
• Each user has at least one program executing in memory -> process
• If several jobs are ready to run at the same time -> CPU scheduling
• If processes don't fit in memory, switching moves them in and out to run
• Virtual memory allows execution or processes not completely in memory

Memory Layout for Multiprogrammed System

• The Operating Systems are at max layout, from processes 1-4, and all at zero

Process Management

• A process is a program in execution
• It is a unit of work in a the system, a program is a passive entity while the process is an active entity
• Processes need resources, such as CPU, memory, I/O, and files, to accomplish the task
• Initialization data is also needed by the processes
• Process termination needs to have the reclaim of any reusable resources

Dual-mode Operation

• Allows the OS to protect itself and other system components via user mode and kernel mode
• Some instructions are given as privileged which only executable in kernel mode

How an Operating System Works

• An operating system is comprised of several components

• These components include command interpreter system, process management, file management, security management, network management, I/O device management, secondary storage management , and main memory management.

Process Management Activities

• The OS needs to create and delete users and systems
• It needs to suspend and resume processes
• There is a need to provide mechanisms for process synchronization
• Mechanisms are also needed for process communication
• Has to provide mechanisms for deadlock handling

Process Management

• Single-threaded process has one program counter specifying location of next instruction to execute
  • Process executes instructions sequentially, one at a time, until completed
• Multi-threaded process has one program counter per thread
• Typically the system has many processes, some user, some operating system running concurrently on one or more CPUs
• Concurrency by multiplexing the CPUs among the processes / threads

Memory Management

• Must execute a program
• All or Part of the instructions must be in memory
• Memory management determines what is in memory and when
• Optimizing CPU utilization and computer response to users
• Memory management activities:
  • Keeping track of which parts of memory are currently being used and by whom
  • Deciding which processes (or parts thereof) and data to move into and out of memory
  • Allocating and deallocating memory space as needed

Mass-Storage Management

• Disks usually used to store data that does not fit in main memory or data that must be kept for a "long" time
• Propper management is of central importance
• Entire speed of computer operation hinges on disk subsystem and its algorithms
  • OS activities
    • Mounting and unmounting
    • Free-space management
    • Storage allocation
    • Disk scheduling
    • Partitioning
    • Protection

Caching

• An important principle performed at many levels in a computer(in hardware, operating system, software)
• Information in use copied from slower to faster storage temporarily
• Faster storage(cache) is checked if information is there
  • If yes, information is stored directly from there, quickly
  • If not, data is copied into cache and used there
• Cache smaller than storage being cached
  • Cache management is important design problem
  • Including cache size and replacement policy

Characteristics of Various Types of Storage

• A table includes the Level 1 to 5, that includes Name, Typical size, Implementation Technology, Access time (ns), Bandwith (MB/sec), Managed by and Backed by

Movement between levels of storage hierarchy

• Explicit or implicit from cache, registers, main memory, solid-state disk and Magnetic disk

Migration of data "A" from Disk to Register

• Environments need to be careful of use that most recent data, no matter where it is stored in storage and hierarchy
  • Include magnetic disk, main memory, cache and hardware resistor
• Multipleprocess enviroments must provide cache coherency such that most or all CPUs have the most recent value in cache
• Distributed enviroment is even more complex
  • It is because several copies of data can exist in enviroment
• Solutions can be covered in another chapter

I/O Subsystem

• The OS hides pecularities of hardware devices from the user
• The goal is device drivers for specific hardware devices
• Memory management of I/O includes buffering, caching, spooling, and general device-driver interface.

File-system Management

• OS provides uniform and logical views for information storage -Abstracts physical properties for to the logical storage unit - file -Each medium controlled by device (disk drives, tape drive) -Varying properties are access speed, capacity, data-transfer rate, and access method
• File-System management -Files are usually organized into directories.
  • Access control on most systems to determine who can access what
  • OS activities -Creating and deleting files and directories -Primitives to manipulate files and directories -Mapping files onto secondary storage -Backup files onto stable(non-volatile) storage media

Protection and Security

• Protection- and mechanism to control processes or users to resources defined by operating systems
• Security- defend the system as the means for internal with external attacks
• Systems first distiguish among users, to determine who can do what -User and group identifier as controls manage each process, file systems to change to effective ID and more rights
• privilege escalation is used, with its all associated files and processes user identities

Virtualization

• Allows OSes to run apps within other OSes, it is a vast and growing industry
• Emulation is used when the source CPU type is different from target type
• Virtualization OS natively compiled for CPU, running guest OSes also natively complied
  • VMM is known for providing services

Cloud Computing (cont.)

• Use cases for laptops and desktops running multiple OSes, for exploration and compatibility
  • Apple laptop running MacOS X hosts a Windows as guest
• Developing apps with multile systems without having other system processes
  • It is known for running natively, there is no host(VMware, citix)

Computing Environments - Virtualization

• Comprised of processes, programming interface, kernel, and hardware (a)
• Comprised of processes, programming interface, kernel, and hardware with virtual machine manager
• Known as interconnected systems

Distributed System

• A collection of separate, possibly heterogeneous, systems networked together
• Network is communications path and TCP/IP is most common
  • Known as local area network
  • Wide area network
  • Metropolitan area networks (MAN)
  • Personal Area Network (PAN)
• Network Operating System provides features within the system across networks
  • Communication scheme allows systems to exchange messages
  • Illusion of a single system, it is related

Computer System Environments

• basic
• mobile
• client server
• peer-peer
• cloud computing
• real time embedded

Basic approach

• stand-alon general purpose machines
  • but blurred as most systems interconnect with others -web access and portials in general -used with all devices
  • use fire wall to protect the internets

Mobile Environments

• Includes handled smartphones, tablets, etc
• Has OS features
  • GPS,
  • Accelerometer, gyroscope
• New types of apps are augmented reality
• use IEEE 802.11 wireless, or cellular data networks for connectivity
• leaders are Apple iOS and Google Android

Client-Server Computing

• Replaced dumb terminals replaced by smart PC
• Many systems now support servers responding to requests generated by clients
  • Compute-server systems provide interface clients to request services
  • File-server systems provide interface to store and retrieve files to clients

Peer to Peer Enviroment

• Many nodes is considered peers
  • may each act as client, server, or both
  • node mush join pee network
  • registers its service with lookup network service
    • Examples include Napster and gnutella, VoIP such as Skype.

Cloud Computing (cont.)

• delivers computing, storage, or even the apps in a service
• Amazon as it is base and the logical extension of virtualizations
• has thousands of servers with millions of virtual machine, it with available of an internet and the pay with is based by usages.

Cloud Computing (cont.)

• Includes: Public cloud, Private cloud, Hybrid cloud, Software as a Service (SaaS), Platform as a Service (PaaS), Infrastructure as a Service (IaaS)

Cloud Computing (cont.)

• cloud computings with the enviroment of the traditonal OS, the VMMs, and also the managenment tools
• the traffic across the many applications
• inter connections access with and the security like firewalls
  • Load Balancers

Real-Time Embedded Systems

• Real-time embedded systems are the most prevalent form of computers
• Vary in considerable and specialized purpose or limited version of the OS for the real time OS
  • Use special expansion
• Some of the special purpose comouts enviroment is many special operating system that that is run in them selves in the environment to run programs -The operating system constraint time constait has well defined

Kernel Data Structures

• Similar to standard programming data structures
  • Singly linked list
  • Doubly linked list
  • Circular linked list

Kernel Data Structures

• Binary search tree: a data structure with left <= right. Search performance is O(n)
• Balanced binary search tree: search performance is O(log n)

More Kernel Data Structures

• Hash function: Can create a hash map when passed a key value
• Bitmap: string of n binary digits representing the status of n items