Chapter 1: Introduction Flashcards
1
Q
What is an Operating System?
A
A program that acts as an intermediary between a user of a computer and the computer hardware
2
Q
(4) What is an Operating System? Operating system goals?
A
- Execute user programs and make solving user problems easier
- Make the computer system convenient to use
- Use the computer hardware in an efficient manner
3
Q
(5)Computer System Structure?what are the components of computer ?
A
1. Hardware – provides basic computing resources: CPU, memory, I/O devices
** 2**. Operating system
Controls and coordinates use of hardware among various applications and users
3. 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
4.Users
People, machines, other computers
4
Q
(6)Four Components of a Computer System diagram ?
A
5
Q
(7)What Operating Systems Do?
A
Depends on the point of view:
- Users want convenience, ease of use
- Don’t care about resource utilization
- But shared computer such as mainframe or minicomputer must keep all users happy
- Users of dedicate systems such as workstations have dedicated resources but frequently use shared resources from servers.
- Handheld computers are resource poor, optimized for usability and battery life
- Some computers have little or no user interface, such as embedded computers in devices and automobiles
6
Q
(8)Operating System Definition?
A
- 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
7
Q
(9)Operating System Definition (Cont.?
A
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.
8
Q
(10)what happens at 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 and starts execution
9
Q
(11)Computer System Organization?
A
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
10
Q
(12)Computer-System Operation
A
- 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
11
Q
(13)Common Functions of Interrupts?
A
- 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
- A trap or exception is a software-generated interrupt caused either by an error or a user request
- An operating system is interrupt driven
12
Q
(14)Interrupt Handling?
A
- 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 interrup
13
Q
(15)Interrupt Timeline diagarm?
A
14
Q
(16)I/O Structure ?
A
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
15
Q
(16)I/O Structure ?
A
After I/O starts, control returns to user program without waiting for I/O completion
- System call – request to the OS 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
- OS indexes into I/O device table to determine device status and to modify table entry to include interrupt
16
Q
(17)Storage Definitions and Notation Review?
what is a bit ?
A
The basic unit of computer storage is the bit. A bit can contain one of two values, 0 and 1. All other storage in a computer is based on collections of bits.
17
Q
(17)Storage Definitions and Notation Review?
what is a byte?
A
A byte is 8 bits, and on most computers it is the smallest convenient chunk of storage. For example, most computers don’t have an instruction to move a bit but do have one to move a byte.
18
Q
(17)Storage Definitions and Notation Review?
what is a word?
A
A less common term is word, which is a given computer architecture’s native unit of data. A word is made up of one or more bytes. For example, a computer that has 64-bit registers and 64-bit memory addressing typically has 64-bit (8-byte) words.
19
Q
(17) A kilobyte, or KB, is
A
1,024 bytes
20
Q
(17)a megabyte, or MB, is
A
1,0242 bytes
21
Q
(17) a gigabyte, or GB, is
A
1,0243 bytes
22
Q
(17) a terabyte, or TB, is a
A
is 1,0244 bytes
23
Q
(17)a petabyte, or PB,
A
is 1,0245 bytes.
24
Q
(17) Networking measurements are an exception to this general rule
A
they are given in bits (because networks move data a bit at a time).
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(18)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
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(18)Storage Structure
* Main memory
* Secondary storage
* Magnetic disks
* Solid-state disks
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(18)Storage Structure-**main memory**?
only large storage media that the CPU can access directly
* **Random access**
* Typically **volatile**
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(1)Storage Structure-**secondary storage **?
extension of main memory that provides large **nonvolatile** storage capacity
29
(19) storage structure- megnatic disk ?
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
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(19)Storage structue-Solid-state disks?
faster than magnetic disks, nonvolatile
* Various technologies
* Becoming more popular
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(20)Storage Hierarchy-Storage systems organized in hierarchy base on?
1. Speed
2. Cost
3. Volatility
32
(20)Storage Hierarchy-Caching?
copying information into faster storage system; main memory can be viewed as a cache for secondary storage
33
(20)Storage Hierarchy-Device Driver is?
for each device controller to manage I/O
Provides uniform interface between controller and kernel
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**(21)Storage-Device Hierarchy Diagram ?**
35
(22) is the important cashing and where why ?
**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
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(23)Computer-System Architecture
Most systems use a single general-purpose processor (PDAs through mainframes)
Most systems have **special-purpose processors** as well
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(23)Computer-System Architecture-**Multiprocessors ?**
systems growing in use and importance
Also known as **parallel systems, tightly-coupled systems**
Advantages include:
1. Increased throughput
2. Economy of scale
3. Increased reliability – graceful degradation or fault tolerance
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**(23)Computer-System Architecture- types of multiprocessors ?**
Two types:
Asymmetric Multiprocessing
Symmetric Multiprocessing
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(24)How a Modern Computer Works ?
40
(25) Symmetric Multiprocessing Architecture
41
(26) A Dual-Core Design** variations ? **
**UMA** and **NUMA** architecture variations
Multi-chip and multicore
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(26) A Dual-Core Design two types of systems ?
Systems containing all chips vs. **blade servers**
Chassis containing multiple separate systems
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(27)Clustered Systems , what are they ?
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
44
(27) clustered systems?types ?
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
45
(27) clustered systems- what are **HPC**?
Some clusters are for **high-performance computing (HPC)**
Applications must be written to use **parallelization**
46
(27) Clustered Systems- how to avoid conflicting operations ?
Some have **distributed lock manager (DLM)** to avoid conflicting operations
47
(28) Clustered Systems- Diagram?
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(29)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
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(29)Operating System Structure-what is** 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
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(30)Memory Layout for Multiprogrammed System Diagram
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(31)Operating-System Operations-i**nterrupts**?
**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
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(31)Operating-System Operations- 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
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(32) Transition from User to Kernel Mode, how is it done ?
**Timer to prevent infinite loop / process 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
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(33) Process Management- Difference btw process and progress ?
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**.
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(33) Process Management-what does a process need resources and termination?
_Process needs resources to accomplish its task:_
* CPU, memory, I/O, files
* Initialization data
_Process termination requires reclaim of any reusable resources_
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(33) process managment - Difference between single thread and multi-threaded porcess ?
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
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(34)Process Management Activities- what are they ?
_ The operating system is responsible for the following activities in connection with process management:_
1. Creating and deleting both user and system processes
2. Suspending and resuming processes
3. Providing mechanisms for process synchronization
4. Providing mechanisms for process communication
5. Providing mechanisms for deadlock handling
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(35)Memory Management- what does the memory holds?
All data in memory before and after processing
All instructions in memory in order to execute
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(35) memory managment- what does it do ?
Memory management determines what is in memory when
* Optimizing CPU utilization and computer response to users
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(36)Storage Management- what does OS provide ?
_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)
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(36) Memory management - what is the file managemnet ?
**File-System management**
Files usually organized into directories
Access control on most systems to determine who can access what
OS activities include :
1. Creating and deleting files and directories
2. Primitives to manipulate files and dirs
3. Mapping files onto secondary storage
4. Backup files onto stable (non-volatile) storage media
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(37)Mass-Storage Management-why use it ?
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 algorithm
OS activities:
1. Free-space management
2. Storage allocation
3. Disk scheduling
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(37)Mass-Storage Management-Tertiary storage ?
Some storage need not be fast
* Tertiary storage includes optical storage, magnetic tape
* Still must be managed – by OS or applications
* Varies between WORM (write-once, read-many-times) and RW (read-write)
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(35) memory managme- what are the activities ?
**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
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(38)Performance of Various Levels of Storage-diagram ?
Movement between levels of storage hierarchy can be explicit or implicit
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(39)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
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(40)I/O Subsystem
One purpose of OS is to hide peculiarities of hardware devices from the user
I/O subsystem responsible for
1. 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)
2. General device-driver interface
3. Drivers for specific hardware devices
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(41)Protection and Security- what are they ?
**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 servic
69
(41)Protection and Security- how to ?
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
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(42)Kernel Data Structures- diagrams?
Many similar to standard programming data structures
71
(43)Kernel Data Structures- biinary search tree ?
**Binary search tree**
left \<= right
Search performance is O(n)
**Balanced binary search tree** is O(lg n)
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(44)Kernel Data Structures-hash function and bit map:?
**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 , ,
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(45)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
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(46)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**
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(47)**Computing Environments – Distributed**
Distributed
* 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
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(48)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
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(49)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
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(50)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 – I**nterpretation**
**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** provides virtualization services
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(51)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)
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(52)Computing Environments - Virtualization Diagram
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(53)Computing Environments – Cloud Computing
Delivers computing, storage, even apps as a service across a network
Logical extension of virtualization as based on virtualization
Amazon **EC2** has thousands of servers, millions of VMs, PBs 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)
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(54)Computing Environments – Cloud Computing
Cloud compute environments composed of traditional OSes, plus VMMs, plus cloud management tools
* Internet connectivity requires security like firewalls
* Load balancers spread traffic across multiple applications
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(55)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
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(56)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** 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
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