CS计算机代考程序代写 distributed system IOS scheme data structure cache android database algorithm concurrency compiler 1.01

1.01

Introduction
What Operating Systems Do
Computer-System Organization
Computer-System Architecture
Operating-System Structure
Operating-System Operations
Process Management
Memory Management
Storage Management
Protection and Security
Distributed Systems
Special-Purpose Systems
Computing Environments
Open-Source Operating Systems

Objectives
To provide a grand tour of the major operating systems components
To provide coverage of basic computer system organization

What is an Operating System?
A program that acts as an intermediary between a user of a computer and the computer hardware
Operating system goals:
Execute user programs and make solving user problems easier
Make the computer system convenient to use
Use the computer hardware in an efficient manner

Computer System Structure
Computer system can be divided into four components
Hardware – provides basic computing resources
CPU, memory, I/O devices
Operating system
Controls and coordinates use of hardware among various applications and users
Application programs – define the ways in which the system resources are used to solve the computing problems of the users
Word processors, compilers, web browsers, database systems, video games
Users
People, machines, other computers

Four Components of a Computer System

Operating System Definition

OS is a resource allocator
Manages all resources
Decides between conflicting requests for efficient and fair resource use
OS is a control program
Controls execution of programs to prevent errors and improper use of the computer

Operating System Definition (Cont)
No universally accepted definition
“Everything a vendor ships when you order an operating system” is good approximation
But varies wildly
“The one program running at all times on the computer” is the kernel. Everything else is either a system program (ships with the operating system) or an application program

Computer Startup
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 and starts execution

Computer System Organization
Computer-system operation
One or more CPUs, device controllers connect through common bus providing access to shared memory
Concurrent execution of CPUs and devices competing for memory cycles

Computer-System Operation
I/O devices and the CPU can execute concurrently
Each device controller is in charge of a particular device type
Each device controller has a local buffer
CPU moves data from/to main memory to/from local buffers
I/O is from the device to local buffer of controller
Device controller informs CPU that it has finished its operation by causing an interrupt

Common Functions of Interrupts
Interrupt transfers control to the interrupt service routine generally, through the interrupt vector, which contains the addresses of all the service routines
Interrupt architecture must save the address of the interrupted instruction
Incoming interrupts are disabled while another interrupt is being processed to prevent a lost interrupt
A trap is a software-generated interrupt caused either by an error or a user request
An operating system is interrupt driven

Interrupt Handling
Device sends electrical signal over its bus to interrupt controller
If interrupt line is enabled, controller sends interrupt to processor (electrical signal over a special pin to the processor)
Processor immediately stops what it’s doing
Disables the interrupt system, (almost) all interrupt lines.
Looks at the interrupt request (IRQ) number.
Consults interrupt vector for interrupt handling routine.
Handles interrupt, i.e., jump to predefined location in memory and executes code there. Predefined location = entry point for interrupt handlers.

Interrupt Handling

Interrupt Handling
The operating system preserves the state of the CPU by storing registers and the program counter
Determines which type of interrupt has occurred:
polling
vectored interrupt system
Separate segments of code determine what action should be taken for each type of interrupt

I/O Structure
After I/O starts, control returns to user program only upon I/O completion
Wait instruction idles the CPU until the next interrupt
Wait loop (contention for memory access)
At most one I/O request is outstanding at a time, no simultaneous I/O processing
After I/O starts, control returns to user program without waiting for I/O completion
System call – request to the operating system to allow user to wait for I/O completion
Device-status table contains entry for each I/O device indicating its type, address, and state
Operating system indexes into I/O device table to determine device status and to modify table entry to include interrupt

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

Storage Structure
Main memory – only large storage media that the CPU can access directly
Random access
Typically volatile
Secondary storage – extension of main memory that provides large nonvolatile storage capacity
Hard disks – rigid metal or glass platters covered with magnetic recording material
Disk surface is logically divided into tracks, which are subdivided into sectors
The disk controller determines the logical interaction between the device and the computer
Solid-state disks – faster than hard disks, nonvolatile
Various technologies
Becoming more popular

Storage-Device Hierarchy

Caching
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) checked first to determine if information is there
If it is, information used directly from the cache (fast)
If not, data copied to cache and used there
Cache smaller than storage being cached
Cache management important design problem
Cache size and replacement policy

Computer-System Architecture
Most systems use a single general-purpose processor (PDAs through mainframes)
Most systems have special-purpose processors as well
Multiprocessors systems growing in use and importance
Also known as parallel systems, tightly-coupled systems
Advantages include

Increased throughput
Economy of scale
Increased reliability – graceful degradation or fault tolerance
Two types

Asymmetric Multiprocessing
Symmetric Multiprocessing

How a Modern Computer Works

Symmetric Multiprocessing Architecture

A Dual-Core Design

Clustered Systems
Like multiprocessor systems, but multiple systems working 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

Operating System Structure

Multiprogramming needed for efficiency
Single user cannot keep CPU and I/O devices busy at all times
Multiprogramming organizes jobs (code and data) so CPU always has one to execute
A subset of total jobs in system is kept in memory
One job selected and run via job scheduling
When it has to wait (for I/O for example), OS switches to another job
Timesharing (multitasking) is logical extension in which CPU switches jobs so frequently that users can interact with each job while it is running, creating interactive computing
Response time should be < 1 second Each user has at least one program executing in memory process If several jobs ready to run at the same time  CPU scheduling If processes don’t fit in memory, swapping moves them in and out to run Virtual memory allows execution of processes not completely in memory Memory Layout for Multiprogrammed System Operating-System Operations Interrupt driven by hardware Software error or request creates exception or trap Division by zero, request for operating system service Other process problems include infinite loop, processes modifying each other or the operating system Dual-mode operation allows OS to protect itself and other system components User mode and kernel mode Mode bit provided by hardware Provides ability to distinguish when system is running user code or kernel code Some instructions designated as privileged, only executable in kernel mode System call changes mode to kernel, return from call resets it to user Increasingly CPUs support multi-mode operations i.e. virtual machine manager (VMM) mode for guest VMs Transition from User to Kernel Mode Timer to prevent infinite looping process from hogging resources Set interrupt after specific period Operating system decrements counter When counter zero generate an interrupt Set up before scheduling process to regain control or terminate program that exceeds allotted time Process Management A process is a program in execution. It is a unit of work within the system. Program is a passive entity, process is an active entity. Process needs resources to accomplish its task CPU, memory, I/O, files Initialization data Process termination requires reclaim of any reusable resources Single-threaded process has one program counter specifying location of next instruction to execute Process executes instructions sequentially, one at a time, until completion Multi-threaded process has one program counter per thread Typically 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 Process Management Activities The operating system is responsible for the following activities in connection with process management: Creating and deleting both user and system processes Suspending and resuming processes Providing mechanisms for process synchronization Providing mechanisms for process communication Providing mechanisms for deadlock handling Memory Management All data in memory before and after processing All instructions in memory in order to execute Memory management determines what is in memory 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 Storage Management OS provides uniform, logical view of information storage Abstracts physical properties to logical storage unit - file Each medium is controlled by device (i.e., disk drive, tape drive) Varying properties include access speed, capacity, data-transfer rate, access method (sequential or random) File-System management Files usually organized into directories Access control on most systems to determine who can access what OS activities include Creating and deleting files and directories Primitives to manipulate files and dirs Mapping files onto secondary storage Backup files onto stable (non-volatile) storage media Mass-Storage Management Usually disks used to store data that does not fit in main memory or data that must be kept for a “long” period of time Proper management is of central importance Entire speed of computer operation hinges on disk subsystem and its algorithms OS activities Free-space management Storage allocation Disk scheduling Some storage need not be fast Tertiary storage includes optical storage, magnetic tape Still must be managed Varies between WORM (write-once, read-many-times) and RW (read-write) Performance of Various Levels of Storage Movement between levels of storage hierarchy can be explicit or implicit Migration of Integer A from Disk to Register Multitasking environments must be careful to use most recent value, no matter where it is stored in the storage hierarchy Multiprocessor environment must provide cache coherency in hardware such that all CPUs have the most recent value in their cache Distributed environment situation even more complex Several copies of a datum can exist Various solutions covered in Chapter 17 I/O Subsystem One purpose of OS is to hide peculiarities of hardware devices from the user I/O subsystem responsible for Memory management of I/O including buffering (storing data temporarily while it is being transferred), caching (storing parts of data in faster storage for performance), spooling (the overlapping of output of one job with input of other jobs) General device-driver interface Drivers for specific hardware devices Protection and Security Protection – any mechanism for controlling access of processes or users to resources defined by the OS Security – defense of the system against internal and external attacks Huge range, including denial-of-service, worms, viruses, identity theft, theft of service Systems generally first distinguish among users, to determine who can do what User identities (user IDs, security IDs) include name and associated number, one per user User ID then associated with all files, processes of that user to determine access control Group identifier (group ID) allows set of users to be defined and controls managed, then also associated with each process, file Privilege escalation allows user to change to effective ID with more rights Computing Environments Traditional computer Blurring over time Office environment PCs connected to a network, terminals attached to mainframe or minicomputers providing batch and timesharing Now portals allowing networked and remote systems access to same resources Home networks Used to be single system, then modems Now firewalled, networked - Many similar to standard programming data structures Singly linked list - Doubly linked list - Circular linked list Kernel Data Structures Binary search tree left <= right Search performance is O(n) Balanced binary search tree is O(lg n) Kernel Data Structures Kernel Data Structures Hash function can create a hash map Bitmap – string of n binary digits representing the status of n items Linux data structures defined in include files , ,

Computing Environments – Traditional
Stand-alone general purpose machines
But blurred as most systems interconnect with others (i.e., the Internet)
Portals provide web access to internal systems
Network computers (thin clients) are like Web terminals
Mobile computers interconnect via wireless networks
Networking becoming ubiquitous – even home systems use firewalls to protect home computers from Internet attacks

Computing Environments – Traditional

Computing Environments – Mobile
Handheld smartphones, tablets, etc
What is the functional difference between them and a “traditional” laptop?
Extra feature – more OS features (GPS, gyroscope)
Allows new types of apps like augmented reality
Use IEEE 802.11 wireless, or cellular data networks for connectivity
Leaders are Apple iOS and Google Android

Computing Environments – Distributed
Distributed computiing
Collection of separate, possibly heterogeneous, systems networked together
Network is a communications path, TCP/IP most common
Local Area Network (LAN)
Wide Area Network (WAN)
Metropolitan Area Network (MAN)
Personal Area Network (PAN)
Network Operating System provides features between systems across network
Communication scheme allows systems to exchange messages
Illusion of a single system

Computing Environments – Client/Server
Client-Server Computing
Dumb terminals supplanted by smart PCs
Many systems now servers, responding to requests generated by clients
Compute-server system provides an interface to client to request services (i.e., database)
File-server system provides interface for clients to store and retrieve files

Computing Environments – Peer-to-Peer
Another model of distributed system
P2P does not distinguish clients and servers
Instead all nodes are considered peers
May each act as client, server or both
Node must join P2P network
Registers its service with central lookup service on network, or
Broadcast request for service and respond to requests for service via discovery protocol
Examples include Napster and Gnutella, Voice over IP (VoIP) such as Skype

Computing Environments – Virtualization
Allows operating systems to run applications within other OSes
Vast and growing industry
Emulation used when source CPU type different from target type (i.e. PowerPC to Intel x86)
Generally slowest method
When computer language not compiled to native code – Interpretation
Virtualization – OS natively compiled for CPU, running guest OSes also natively compiled
Consider VMware running WinXP guests, each running applications, all on native WinXP host OS
VMM (virtual machine Manager) provides virtualization services

Computing Environments – Virtualization
Use cases involve laptops and desktops running multiple OSes for exploration or compatibility
Apple laptop running Mac OS X host, Windows as a guest
Developing apps for multiple OSes without having multiple systems
QA testing applications without having multiple systems
Executing and managing compute environments within data centers
VMM can run natively, in which case they are also the host
There is no general purpose host then (VMware ESX and Citrix XenServer)

Computing Environments – Virtualization

Computing Environments – Cloud Computing
Delivers computing, storage, even apps as a service across a network
Logical extension of virtualization because it uses virtualization as the base for it functionality.
Amazon EC2 has thousands of servers, millions of virtual machines, petabytes of storage available across the Internet, pay based on usage
Many types
Public cloud – available via Internet to anyone willing to pay
Private cloud – run by a company for the company’s own use
Hybrid cloud – includes both public and private cloud components
Software as a Service (SaaS) – one or more applications available via the Internet (i.e., word processor)
Platform as a Service (PaaS) – software stack ready for application use via the Internet (i.e., a database server)
Infrastructure as a Service (IaaS) – servers or storage available over Internet (i.e., storage available for backup use)

Computing Environments – Cloud Computing
Cloud computing environments composed of traditional OSes, plus VMMs, plus cloud management tools
Internet connectivity requires security like firewalls
Load balancers spread traffic across multiple applications

Computing Environments – Real-Time Embedded Systems
Real-time embedded systems most prevalent form of computers
Vary considerable, special purpose, limited purpose OS, real-time OS
Use expanding
Many other special computing environments as well
Some have OSes, some perform tasks without an OS
Real-time OS has well-defined fixed time constraints
Processing must be done within constraint
Correct operation only if constraints met

Open Source OS
Operating systems made available in source-code format rather than just binary closed-source
Counter to the copy protection and Digital Rights Management (DRM) movement
Started by Free Software Foundation (FSF), which has “copyleft” GNU Public License (GPL)
Examples include GNU/Linux and BSD UNIX (including core of Mac OS X), and many more
Can use VMM like VMware Player (Free on Windows), Virtualbox (open source and free on many platforms – http://www.virtualbox.com)
Use to run guest operating systems for exploration

Open-Source Operating Systems
Operating systems made available in source-code format rather than just binary closed-source
Counter to the copy protection and Digital Rights Management (DRM) movement
Started by Free Software Foundation (FSF), which has “copyleft” GNU Public License (GPL)
Examples include GNU/Linux, BSD UNIX (including core of Mac OS X), and Sun Solaris

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