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Distributed Computing Systems CSCI 6900/4900 Review Design goals Resource availability to users Transparency Openness Scalability Security and privacy Hardware concepts Multiprocessors Vs. Multicomputers Bus-based Vs. Switch-based Homogenous Vs. Heterogenous Software Concepts

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Presentation Transcript
review
Review
  • Design goals
    • Resource availability to users
    • Transparency
    • Openness
    • Scalability
    • Security and privacy
  • Hardware concepts
    • Multiprocessors Vs. Multicomputers
    • Bus-based Vs. Switch-based
    • Homogenous Vs. Heterogenous
software concepts
Software Concepts
  • Functionalities
    • Resource managers
    • Hiding intricacies and heterogeneity
  • Two kinds of operating systems
    • Tightly coupled (distributed operating system)
    • Loosely coupled (network operating system)
  • Middleware
    • Providing transparency for loosely coupled systems
uniprocessor operating systems
Uniprocessor Operating Systems
  • Virtualize physical devices (manages devices, protects users)
  • Two modes (User, Kernel)
  • Two kinds (Monolithic, microkernel)

1.11

  • Separating applications from operating system code through
  • a microkernel.
multiprocessor operating systems
Multiprocessor Operating Systems
  • Similar in many aspects to uni-processor systems
  • Main extension is how shared memory access is handled
    • Guard against simultaneous access to provide consistency
  • Two primitives
    • Semaphores
      • Two atomic primitives (UP and DOWN)
    • Monitors
monitors
Monitors

monitor Counter {

private:

int count = 0;

public:

int value() { return count;}

void incr () { count = count + 1;}

void decr() { count = count – 1;}

}

  • Borrowed from programming languages
  • Has data and procedures
  • One process can execute at any point of time
monitors 2
Monitors (2)

monitor Counter {

private:

int count = 0;

int blocked_procs = 0;

condition unblocked;

public:

int value () { return count;}

void incr () {

if (blocked_procs == 0)

count = count + 1;

else

signal (unblocked);

}

void decr() {

if (count ==0) {

blocked_procs = blocked_procs + 1;

wait (unblocked);

blocked_procs = blocked_procs – 1;

}

else

count = count – 1;

}

}

  • Monitors can be used to conditionally block processes
  • Producers/consumers scenario
multicomputer operating systems
Multicomputer Operating Systems

1.14

  • Communication is only through message passing
  • Layer on top of local kernels for coordination and management of remote resources
multicomputer operating systems 2
Multicomputer Operating Systems (2)

1.15

  • Two buffering places
  • Four blocking points for sender (S1, S2, S3, S4)
  • One blocking point for receiver (S3)
communication reliability synchronization
Communication Reliability & Synchronization
  • Message passing semantics also depends upon reliability of communication
distributed shared memory systems 1
Distributed Shared Memory Systems (1)
  • Programming harder without the notion of shared address space
  • DSM emulates shared memory using message passing primitives
  • Pages of address space distributed among four machines
  • Situation after CPU 1 references page 10
  • Situation if page 10 is read only and replication is used
effect of page size on dsm performance
Effect of Page Size on DSM Performance

1.18

  • Cost of page transfer is dominated by setup costs
  • False sharing results in unnecessary data transfers
network operating system
Network Operating System

1-19

  • Collection of heterogeneous systems
  • Facilitates users to access services on specific machines (rlogin, rcp, etc.)
network operating system 2
Network Operating System (2)

1-20

  • Global file systems facilitate convenient data sharing
  • File servers execute requests and send replies
global file systems
Global File Systems

1.21

  • Different clients may mount the servers in different places.
dos vs nos
DOS Vs. NOS
  • DOS
    • Transparency
    • Ease of use & security
  • NOS
    • Scalability
    • Openness
  • Can we have best of both worlds?
middleware
Middleware
  • Layer on top of Network OS services
  • Hide heterogeneity
  • Doesn’t manage individual nodes
  • Provides complete set of services
middleware models services
Middleware Models & Services
  • Models
    • File model
    • Distributed file systems
    • Remote procedure calls
    • Distributed objects
    • Distributed document systems
  • Services
    • Communication facilities
    • Naming
    • Persistence
    • Transactions
middleware and openness
Middleware and Openness
  • Common protocols
  • Common interfaces
  • Completeness
comparison between systems
Comparison between Systems
  • A comparison between multiprocessor operating systems, multicomputer operating systems, network operating systems, and middleware based distributed systems.