Lecture 8: Operating Systems Structures

Lecture 8: Operating Systems Structures

CS162 Operating Systems and Systems Programming Lecture 2 History of the World Parts 15 Operating Systems Structures September 3rd, 2008 Prof. John Kubiatowicz http://inst.eecs.berkeley.edu/~cs162 Review: Virtual Machine Abstraction Application Operating System Virtual Machine Interface Physical Machine Interface Hardware Software Engineering Problem: Turn hardware/software quirks what programmers want/need Optimize for convenience, utilization, security, reliability, etc

For Any OS area (e.g. file systems, virtual memory, networking, scheduling): Whats the hardware interface? (physical reality) Whats the application interface? (nicer abstraction) 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.2 Goals for Today Finish Protection Example History of Operating Systems Really a history of resource-driven choices Operating Systems Structures Operating Systems Organizations Abstractions and layering Note: Some slides and/or pictures in the following are adapted from slides 2005 Silberschatz, Galvin, and 9/03/08 Kubiatowicz CS162 UCB

Fall 2008 Lec 2.3 Gagne Many slides Gagne. generated from lecture notes by Example: Protecting Processes from Each Other Problem: Run multiple applications in such a way that they are protected from one another Goal: Keep User Programs from Crashing OS Keep User Programs from Crashing each other [Keep Parts of OS from crashing other parts?] (Some of the required) Mechanisms: Address Translation Dual Mode Operation Simple Policy: Programs are not allowed to read/write memory of other Programs or of Operating System 9/03/08

Kubiatowicz CS162 UCB Fall 2008 Lec 2.4 Example: Address Translation Address Space A group of memory addresses usable by something Each program (process) and kernel has potentially different address spaces. Address Translation: Translate from Virtual Addresses (emitted by CPU) into Physical Addresses (of memory) Mapping often performed in Hardware by Memory Management Unit (MMU) CPU 9/03/08 Virtual Addresses MMU

Physical Addresses Kubiatowicz CS162 UCB Fall 2008 Lec 2.5 Example: Example of Address Translation Data 2 Code Data Heap Stack Code Data Heap Stack Stack 1 Heap 1 Code 1 Stack 2

Prog 1 Virtual Address Space 1 Prog 2 Virtual Address Space 2 Data 1 Heap 2 Code 2 OS code Translation Map 1 OS data Translation Map 2 OS heap & Stacks 9/03/08

Physical Address Space Kubiatowicz CS162 UCB Fall 2008 Lec 2.6 Example: Dual Mode Operation Hardware provides at least two modes: Kernel mode (or supervisor or protected) User mode: Normal programs executed Some instructions/ops prohibited in user mode: Example: cannot modify page tables in user mode Attempt to modify Exception generated Transitions from user mode to kernel mode: System Calls, Interrupts, Other exceptions 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.7

UNIX System Structure User Mode Applications Standard Libs Kernel Mode Hardware 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.8 Moores Law Change Drives OS Change CPU MHz, Cycles/inst DRAM capacity Disk capacity Net

bandwidth # addr bits #users/ machine Price 1981 10 310 128KB 2006 3200x4 0.25 0.5 4GB Factor 1,280 640 32,768 10MB 9600 b/ s 16

1TB 100,000 1 Gb/s 110,000 32 2 10s 1 0.1 $25,000 $4,000 0.2 Typical academic computer 1981 vs 2006

9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.9 Moores law effects Nothing like this in any other area of business Transportation in over 200 years: 2 orders of magnitude from horseback @10mph to Concorde @1000mph Computers do this every decade (at least until 2002)! What does this mean for us? Techniques have to vary over time to adapt to changing tradeoffs I place a lot more emphasis on principles The key concepts underlying computer systems Less emphasis on facts that are likely to change over the next few years Lets examine the way changes in $/MIP has radically changed how OSs work 9/03/08

Kubiatowicz CS162 UCB Fall 2008 Lec 2.10 Dawn of time ENIAC: (19451955) The machine designed by Drs. Eckert and Mauchly was a monstrosity. When it was finished, the ENIAC filled an entire room, weighed thirty tons, and consumed two hundred kilowatts of power. http://ei.cs.vt.edu/~history/ENIAC.Richey.HTML 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.11 History Phase 1 (19481970) Hardware Expensive, Humans Cheap When computers cost millions of $s, optimize for more efficient use of the hardware! Lack of interaction between user and computer

User at console: one user at a time Batch monitor: load program, run, print Optimize to better use hardware When user thinking at console, computer idleBAD! Feed computer batches and make users wait Autograder for this course is similar No protection: what if batch program has bug? 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.12 Core Memories (1950s & 60s) The first magnetic core memory, from the IBM 405 Alphabetical Accounting Machine. Core Memory stored data as magnetization in iron rings Iron cores woven into a 2-dimensional mesh of wires

Origin of the term Dump Core Rumor that IBM consulted Life Saver company See: http://www.columbia.edu/acis/history/core.html 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.13 History Phase 1 (late 60s/early 70s) Data channels, Interrupts: overlap I/O and compute DMA Direct Memory Access for I/O devices I/O can be completed asynchronously Multiprogramming: several programs run simultaneously Small jobs not delayed by large jobs More overlap between I/O and CPU Need memory protection between programs and/or OS Complexity gets out of hand: Multics: announced in 1963, ran in 1969

1777 people contributed to Multics (30-40 core dev) Turing award lecture from Fernando Corbat (key researcher): On building systems that will fail OS 360: released with 1000 known bugs (APARs) Anomalous Program Activity Report OS finally becomes an important science: How to deal with complexity??? UNIX based on Multics, but vastly simplified 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.14 A Multics System (Circa 1976) The 6180 at MIT IPC, skin doors open, circa 1976: We usually ran the machine with doors open so the operators could see the AQ register display, which gave you an idea of the machine load, and for convenient access to the EXECUTE button, which the operator would push to enter BOS if the machine crashed.

http://www.multicians.org/multics-stories.html 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.15 Early Disk History 1973: 1. 7 Mbit/sq. in 140 MBytes 9/03/08 1979: 7. 7 Mbit/sq. in 2,300 MBytes Contrast: Seagate 1TB, 164 GB/SQ in, 3 in disk, Kubiatowicz CS162 UCB Fall 2008 4 platters

Lec 2.16 Administrivia Cs162-xx accounts: Make sure you got an account form We have more forms for those of you who didnt get one If you havent logged in yet, you need to do so Nachos readers: TBA: Will be down at Copy Central on Hearst Will include lectures and printouts of all of the code Video Screencast archives available off lectures page Just click on the title of a lecture for webcast Only works for lectures that I have already given! No slip days on first design document for each phase Need to get design reviews in on time Dont know Java well? Talk CS 9G self-paced Java course 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.17

Administriva: Time for Project Signup Project Signup: Watch Group/Section Assignment Link 4-5 members to a group Everyone in group must be able to actually attend same section The sections assigned to you by Telebears are temporary! Only submit once per group! Everyone in group must have logged into their cs162xx accounts once before you register the group Make sure that you select at least 2 potential sections Due tomorrow: Thursday 9/4 by 11:59pm Sections: Sectio Watch for section assignments Time Locationnext Monday TA n Attend new sections next week Tu 11:00Andrey 101 B56 Hildebrand 12:00P Ermolinskiy

102 Tu 1:00-2:00P B56 Hildebrand Jon Whiteaker Andrey 103 Tu 2:00-3:00P 87 Evans 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.18 Ermolinskiy History Phase 2 (1970 1985) Hardware Cheaper, Humans Expensive Swapping, queueing Response time Computers available for tens of thousands of dollars instead of millions OS Technology maturing/stabilizing

Interactive timesharing: Use cheap terminals (~$1000) to let multiple users interact with the system at the same time Sacrifice CPU time to get better response time Users do debugging, editing, and email online Problem: Thrashing Performance very non-linear response with load Thrashing caused by many factors including Users 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.19 The ARPANet (1968-1970s) SRI 940 IMPs Utah PDP 10 UCSB

IBM 360 UCLA Sigma 7 BN team that implemented he interface message processor Paul Baran RAND Corp, early 1960s Communications networks that would survive a major enemy attack ARPANet: Research vehicle for Resource Sharing Computer Networks 2 September 1969: UCLA first node on the ARPANet December 1969: 4 nodes connected by 56 kbps phone lines 1971: First Email 1970s: <100 computers

9/03/08 Kubiatowicz CS162 UCB Fall 2008 ttp://www.cnn.com/2004/TECH/internet/08/29/internet.birthday.ap/index.html Lec 2.20 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.21 ARPANet Evolves into Internet First E-mail SPAM message: 1 May 1978 12:33 EDT 80-83: TCP/IP, DNS; ARPANET and MILNET split 85-86: NSF builds NSFNET as backbone, links 6 Supercomputer centers, 1.5 Mbps, 10,000 computers 87-90: link regional networks, NSI (NASA), ESNet (DOE), DARTnet, TWBNet (DARPA), 100,000 computers ARPANet SATNet PRNet 1965

TCP/IP 1975 NSFNet Deregulation & ISP Commercialization ASP AIP WWW 1985 1995 2005 SATNet: Satelite network PRNet: Radio Network 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.22 What is a Communication Network? (End-system Centric View)

Network offers one basic service: move information Bird, fire, messenger, truck, telegraph, telephone, Internet Another example, transportation service: move objects Horse, train, truck, airplane ... What distinguish different types of networks? The services they provide What distinguish the services? Latency Bandwidth Loss rate Number of end systems Service interface (how to invoke the service?) Others Reliability, unicast vs. multicast, real-time...

9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.23 What is a Communication Network? (Infrastructure Centric View) Communication medium: electron, photon Network components: Links carry bits from one place to another (or maybe multiple places): fiber, copper, satellite, Interfaces attach devices to links Switches/routers interconnect links: electronic/optic, crossbar/Banyan Hosts communication endpoints: workstations, PDAs, cell phones, toasters Protocols rules governing communication between nodes TCP/IP, ATM, MPLS, SONET, Ethernet, X.25 Applications: Web browser, X Windows, FTP, ... 9/03/08 Kubiatowicz CS162 UCB Fall 2008

Lec 2.24 Network Components (Examples) Links Interfaces Fibers Ethernet card Switches/routers Large router Wireless card Coaxial Cable 9/03/08 Telephone switch Kubiatowicz CS162 UCB Fall 2008

Lec 2.25 Types of Networks Geographical distance Local Area Networks (LAN): Ethernet, Token ring, FDDI Metropolitan Area Networks (MAN): DQDB, SMDS Wide Area Networks (WAN): X.25, ATM, frame relay Caveat: LAN, MAN, WAN may mean different things Service, network technology, networks Information type Data networks vs. telecommunication networks Application type Special purpose networks: airline reservation network, banking network, credit card network, telephony General purpose network: Internet 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.26

History Phase 3 (1981 ) Hardware Very Cheap, Humans Very Expensive Computer costs $1K, Programmer costs $100K/year If you can make someone 1% more efficient by giving them a computer, its worth it! Use computers to make people more efficient Personal computing: Computers cheap, so give everyone a PC Limited Hardware Resources Initially: OS becomes a subroutine library One application at a time (MSDOS, CP/M, ) Eventually PCs become powerful: OS regains all the complexity of a big OS multiprogramming, memory protection, etc (NT,OS/ 2) Question: As hardware gets cheaper does need for OS go away? 9/03/08 Kubiatowicz CS162 UCB Fall 2008

Lec 2.27 History Phase 3 (cont) Graphical User Interfaces Xerox Star CS160 All about GUIs Xerox Star: 1981 Originally a research project (Alto) First mice, windows Apple Lisa/Machintosh: 1984 Look and Feel suit 1988 Microsoft Windows: Win 1.0 (1985) Single Win 3.1 (1990) Level Win 95 (1995) Win NT (1993) HAL/Protection Win 2000 (2000) No HAL/ Win XP (2001) Full Prot

Win Vista (2007) Windows 3.1 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.28 History Phase 4 (1988): Distributed Systems Networking (Local Area Networking) Different machines share resources Printers, File Servers, Web Servers Client Server Model Services Computing File Storage 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.29

History Phase 4 (1988): Internet Developed by the research community Based on open standard: Internet Protocol Internet Engineering Task Force (IETF) Technical basis for many other types of networks Intranet: enterprise IP network Services Provided by the Internet Shared access to computing resources: telnet (1970s) Shared access to data/files: FTP, NFS, AFS (1980s) Communication medium over which people interact email (1980s), on-line chat rooms, instant messaging (1990s) audio, video (1990s, early 00s) Medium for information dissemination 9/03/08 USENET (1980s)

WWW (1990s) Audio, video (late 90s, early 00s) replacing radio, TV? File sharing (late 90s, early 00s) Kubiatowicz CS162 UCB Fall 2008 Lec 2.30 Network Cloud 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.31 Regional Nets + Backbone Regional Net Regional Net Backbone Regional

Net Regional Net LAN LAN Regional Net Regional Net LAN LAN: Local Area Network 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.32 Backbones + NAPs + ISPs ISP

ISP NAP NAP ISP Backbones Business ISP LAN LAN ISP Consumer ISP LAN Dial-up SP: Internet Service Provide

NAP: Network Access Point 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.33 Parallel Backbones Digex Backbone Qwest IP Backbone (Late 199 GTE Internetworking Backbone 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.34 Computers Inside the Core DSL Always on

Cable Head Ends @home Covad Cingular Cell Cell Cell LAN 9/03/08 NAP NAP ISP Satellite Fixed Wireless Sprint LAN

AOL LAN Dial-up Kubiatowicz CS162 UCB Fall 2008 Lec 2.35 The Morris Internet Worm (1988) Internet worm (Self-reproducing) Author Robert Morris, a first-year Cornell grad student Launched close of Workday on November 2, 1988 Within a few hours of release, it consumed resources to the point of bringing down infected machines Techniques Exploited UNIX networking features (remote access) Bugs in finger (buffer overflow) and sendmail programs (debug mode allowed remote login) Dictionary lookup-based password cracking Grappling hook program uploaded main worm program 9/03/08

Kubiatowicz CS162 UCB Fall 2008 Lec 2.36 LoveLetter Virus (May 2000) E-mail message with VBScript (simplified Visual Basic) Relies on Windows Scripting Host Enabled by default in Win98/2000 User clicks on attachment infected! E-mails itself to everyone in Outlook address book Replaces some files with a copy of itself Searches all drives Downloads password cracking program 60-80% of US companies infected and 100K European servers 9/03/08

Kubiatowicz CS162 UCB Fall 2008 Lec 2.37 History Phase 5 (1995): Mobile Systems Ubiquitous Mobile Devices Laptops, PDAs, phones Small, portable, and inexpensive Recently twice as many smart phones as PDAs Many computers/person! Limited capabilities (memory, CPU, power, etc) Wireless/Wide Area Networking Leveraging the infrastructure Huge distributed pool of resources extend devices Traditional computers split into pieces. Wireless keyboards/mice, CPU distributed, storage remote Peer-to-peer systems Many devices with equal responsibilities work together Components of Operating System spread across globe

9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.38 CITRISs Model: A Societal Scale Information System Center for Information Technology Research in the Interest of Society The Network is the OS Functionality spread throughout network Massive Cluster Clusters Gigabit Ethernet Scalable, Reliable, Secure Services Mobile, Ubiquitous Systems MEMS for

Sensor Nets 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.39 Datacenter is the Computer (From Luiz Barrosos talk at RAD Lab 12/11) Google program == Web search, Gmail, Google computer == Thousands of computers, networking, storage Warehouse-sized facilities and workloads may be unusual today but are likely to be more common in the next few years 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.40 Migration of Operating-System Concepts and Features

9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.41 History of OS: Summary Change is continuous and OSs should adapt Not: look how stupid batch processing was But: Made sense at the time Situation today is much like the late 60s [poll] Small OS: 100K lines Large OS: 10M lines (5M for the browser!) 100-1000 people-years Complexity still reigns NT developed (early to late 90s): Never worked well Windows 2000/XP: Very successful Windows Vista (aka Longhorn) delayed many times Finally released in January 2007 Promised by removing some of the intended technology Slow adoption rate, even in 2008

CS162: understand OSs to simplify them 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.42 Now for a quick tour of OS Structures 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.43 Operating Systems Components (What are the pieces of the OS)

9/03/08 Process Management Main-Memory Management I/O System management File Management Networking User Interfaces Kubiatowicz CS162 UCB Fall 2008 Lec 2.44 Operating System Services (What things does the OS do?) Services that (more-or-less) map onto components Program execution How do you execute concurrent sequences of instructions? I/O operations Standardized interfaces to extremely diverse devices File system manipulation How do you read/write/preserve files? Looming concern: How do you even find files???

Communications Networking protocols/Interface with CyberSpace? Cross-cutting capabilities Error detection & recovery Resource allocation Accounting Protection 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.45 System Calls (What is the API) See Chapter 2 of 7th edition or Chapter 3 of 6th 9/03/08

Kubiatowicz CS162 UCB Fall 2008 Lec 2.46 Operating Systems Structure (What is the organizational Principle?) Simple Only one or two levels of code Layered Lower levels independent of upper levels Microkernel OS built from many user-level processes Modular Core kernel with Dynamically loadable modules 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.47

Simple Structure MS-DOS written to provide the most functionality in the least space Not divided into modules Interfaces and levels of functionality not well separated 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.48 UNIX: Also Simple Structure UNIX limited by hardware functionality Original UNIX operating system consists of two separable parts: Systems programs The kernel Consists of everything below the system-call interface and above the physical hardware Provides the file system, CPU scheduling, memory management, and other operatingsystem functions; Many interacting functions for one level

9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.49 UNIX System Structure User Mode Applications Standard Libs Kernel Mode Hardware 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.50 Layered Structure Operating system is divided many layers (levels) Each built on top of lower layers

Bottom layer (layer 0) is hardware Highest layer (layer N) is the user interface Each layer uses functions (operations) and services of only lower-level layers Advantage: modularity Easier debugging/Maintenance Not always possible: Does process scheduler lie above or below virtual memory layer? Need to reschedule processor while waiting for paging May need to page in information about tasks Important: Machine-dependent vs independent layers Easier migration between platforms Easier evolution of hardware platform Good idea for you as well! 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.51 Layered Operating System 9/03/08

Kubiatowicz CS162 UCB Fall 2008 Lec 2.52 Microkernel Structure Moves as much from the kernel into user space Small core OS running at kernel level OS Services built from many independent user-level processes Communication between modules with message passing Benefits: Easier to extend a microkernel Easier to port OS to new architectures More reliable (less code is running in kernel mode) Fault Isolation (parts of kernel protected from other parts) More secure

Detriments: Performance overhead severe for nave implementation 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.53 Modules-based Structure Most modern operating systems implement modules Uses object-oriented approach Each core component is separate Each talks to the others over known interfaces Each is loadable as needed within the kernel Overall, similar to layers but with more flexible 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.54

Partition Based Structure for Multicore chips? Firewall Virus Large Compute-BoundIntrusion Application Monitor And Adapt Real-Time Application Identity Persistent Storage & File System Video & Window Drivers HCI/ Device Voice

Drivers Rec Normal Components split into pieces Device drivers (Security/Reliability) Network Services (Performance) TCP/IP stack Firewall Virus Checking Intrusion Detection Persistent Storage (Performance, Security, Reliability) Monitoring services Performance counters Introspection

Identity/Environment services (Security) Biometric, GPS, Possession Tracking 9/03/08 Applications Given Larger Partitions Freedom to use resources arbitrarily Kubiatowicz CS162 UCB Fall 2008 Lec 2.55 Implementation Issues (How is the OS implemented?) Policy vs. Mechanism Policy: What do you want to do? Mechanism: How are you going to do it? Should be separated, since both change Algorithms used Linear, Tree-based, Log Structured, etc Event models used

threads vs event loops Backward compatability issues Very important for Windows 2000/XP System generation/configuration How to make generic OS fit on specific hardware 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.56 Conclusion Rapid Change in Hardware Leads to changing OS Batch Multiprogramming Timeshare Graphical UI Ubiquitous Devices Cyberspace/Metaverse/?? OS features migrated from mainframes PCs Standard Components and Services

Process Control Main Memory I/O File System UI Policy vs Mechanism Crucial division: not always properly separated! Complexity is always out of control However, Resistance is NOT Useless! 9/03/08 Kubiatowicz CS162 UCB Fall 2008 Lec 2.57

Recently Viewed Presentations

  • PowerPoint Template - Virginia

    PowerPoint Template - Virginia

    Without further ado, I will kick this to Karin and Tiffany who will present their findings, and I will jump back in with our suggested recommendations, based on those findings, at the end. Kinship Diversion Qualitative Research-Virginia Findings. Allen &...
  • Best Practices in Geometry - Mr. Miguez&#x27;s Science Class

    Best Practices in Geometry - Mr. Miguez's Science Class

    I have students write up labs in their lab notebook. Although they work in groups, they each must produce their own work using shared data. Labs always have a data table and graph. Dissections are done after the EOC exam....
  • ACT Power Plus Vocabulary - calhoun.k12.al.us

    ACT Power Plus Vocabulary - calhoun.k12.al.us

    Synonyms indifferent offhand Antonyms diligent attentive baroque (adj.) - overly decorated The new dance club had a great light show; the baroque furnishings seemed right in place. ornate Synonyms Antonyms simple hedonism (noun) - pursuit of pleasure, especially of the...
  • Schulungsunterlagen der AG RDA - Wiki

    Schulungsunterlagen der AG RDA - Wiki

    Beschreibung der Reproduktion. Die Informationsquelle für die Reproduktion ist die bevorzugte Informationsquelle. Es werden in den Elementen zur Beschreibung der Manifestation immer die Angaben aufgeführt, die sich auf die Reproduktion beziehen.
  • Whats New & Cool in Surgery: Wheres the

    Whats New & Cool in Surgery: Wheres the

    Lap paraesophageal hernia repair. Lap cancer staging/lymph node biopsy. Lap emergency surgery (bowel obstruction, ulcer, trauma) YES! But, can this type of surgery be done with only one incision? ... PowerPoint Presentation Last modified by:
  • Interactions in regression models: An introduction

    Interactions in regression models: An introduction

    Specification errors for interaction models: Implications for the shape of the overall pattern Jane E. Miller, PhD The Chicago Guide to Writing about Multivariate Analysis, 2nd Edition.
  • Kotler Keller 2 - (MBA)-Human Resource Management

    Kotler Keller 2 - (MBA)-Human Resource Management

    Title: Kotler Keller 2 Author: Tracy Tuten Last modified by: UKASHKI Created Date: 4/2/2006 5:59:30 PM Document presentation format: On-screen Show
  • Network Design and Management - Pearson Education

    Network Design and Management - Pearson Education

    Network Design and Management Topics. Quality of service (QoS) Network design. Network visibility (SNMP) You can't manage what you don't understand. Network visibility is a term that refers to the effects of tools to reveal what the network is doing...