Chapter 11 Modern Computer Systems, Clusters, and Networks

Chapter 11Modern Computer Systems, Clusters, and Networks

The Architecture of Computer Hardware and Systems Software:

An Information Technology Approach

3rd Edition, Irv Englander

John Wiley and Sons 2003

Chapter 11: Modern Computer Systems, Clusters, and Networks

11-2

Basic Personal Computer System


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Mainframe Computer System


11-4

Major PC System Components


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System Performance Improvements Multiple CPUs Faster clock speed, buses and circuits Wider instruction and data paths Faster disk access More and faster memory


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Multiprocessing

Reasons Increase the processing power of a system Parallel processing

Types of multiprocessor systems Tightly coupled systems Loosely coupled systems


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Tightly Coupled Systems

Also called multiprocessor systems Identical access to programs, data,

shared memory, I/O, etc. Easily extends multi-tasking, and

redundant program execution Two ways to configure

Master-slave multiprocessing Symmetrical multiprocessing (SMP)


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Tightly Coupled Systems


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Master-Slave Multiprocessing

Master CPU Manages the system Controls all resources and scheduling Assigns tasks to slave CPUs

Advantages Simplicity Protection of system and data

Disadvantages Master CPU becomes a bottleneck Reliability issues – if master CPU fails entire

system fails


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Symmetrical Multiprocessing

Each CPU has equal access to resources Each CPU determines what to run using a

standard algorithm Disadvantages

Resource conflicts – memory, i/o, etc. Complex implementation

Advantages High reliability Fault tolerant support is straightforward Balanced workload


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Loosely Coupled Systems

Clusters or multi-computer systems Each system has its own CPU, memory, and

I/O facilities Each system is known as a node of the

cluster Advantages

Fault-tolerant, scalable, well balanced, distance is not an issue

Two ways to configure Shared-nothing model Shared-disk model


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Shared-Nothing Model

High speed link between nodes No sharing of resources Partitioning of work through division of

data Advantage

Reduced communication between nodes

Disadvantage Can result in inefficient division of work


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Shared-Disk Model

High speed link between nodes Disk drives are shared between nodes Advantage

Better load balancing

Disadvantage Complex software required for

transactional processing (lock, commit phases)


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Cluster Models


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Beowulf Clusters Simple and highly configurable Low cost Networked

Computers connected to one another by a private Ethernet network

Connection to an external network is through a single gateway computer

Configuration COTS – Commodity-off-the-shelf components such as

inexpensive computers Blade components – computers mounted on a motherboard

that are plugged into connectors on a rack Either shared-disk or shared-nothing model


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Blade and Rack of Beowulf Cluster

Figure 11.9


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Computer Interconnection Communication channel – pathway for data

movement between computers Point-to-Point connectivity

Communication channel that passes data directly between two computers

Serial connection Telephone modem Terminal controller – handles multiple point-to-point

connections for a host computer Multipoint connectivity

Multidrop channel or shared communication channel


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Example: Point-to-Point


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Client-Server Architecture

Computer servers provides services File storage, databases, printing services,

login services, web services

Client computers Execute programs in its own memory Access files either locally or can request

files from a server


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Client-Server Network


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LAN Topology

Arrangement of workstations in a shared medium environment

Logical arrangement (data flow) Physical arrangement (cabling scheme)


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LAN Topologies: Bus

Multipoint medium Stations attach to linear medium (bus)

using tap Transmission from any stations travels

entire medium (both directions) Termination required at ends of bus to

prevent the signal from bouncing Break in cable brings down entire bus


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Bus LAN Diagram


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LAN Topologies: Tree

Generalization of bus topology Branching cable with no closed loops Cable(s) begin at headend, travel to

branches which may have branches of their own

Each transmission propagates through network, can be received by any station


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LAN Topologies: Ring

Repeaters are joined by unidirectional point-to-point links in a ring

As data circulates past a receiver, the receiver checks its address, and copies those intended for it into a local buffer

Data circulates until it returns to source, which removes it from network

Better performance at high levels of usage


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Ring LAN Diagram


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LAN Topologies: Star

Each station connected point-to-point to a central station, usually with two undirectional links

Switching in the central station connects pairs of nodes together

Central node can broadcast info, or can switch frames among stations

Failure of central station causes entire network to go down


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Star LAN Diagram


11-29

Ethernet MAC Protocol

MAC – Medium Access Control Ethernet and CSMA/CD

Carrier sense multiple access with collision detection

Four step procedure If medium is idle, transmit If medium is busy, listen until idle and then transmit If collision is detected, cease transmitting After a collision, wait a random amount of time

before retransmitting


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Ethernet Frame


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Switched Ethernet


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Token Ring MAC Protocol

Token “seized” by changing a bit on the circulating frame to indicate start of frame rather than token

Default configuration requires sender to complete transmission and begin receiving transmitted frame before releasing the token

“Early token release” allows release of token after transmission but before receipt of frame


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Hubs

The active central element of the star layout.

When a single station transmits, the hub repeats the signal on the outgoing line to each station.

Hubs can be cascaded in a hierarchical configuration

Ethernet hubs are physically a star but logically a bus.


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Bridges

Allow connections between LANs and to WANs

Used between similar networks Read all frames from each network Accept frames from sender on one network

that are addressed to a receiver on the other network

Retransmit frames from sender using MAC protocol for receiver


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Routers

Similar to bridges but connect dissimilar networks

Convert format of the message to correspond to the protocol of the other network

Network traffic is specifically addressed to the router


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Wide Area Network Circuit switching

Dedicated channel between source and destination for duration of connection

Message switching Dedicated channel for an entire message

Packet switching An independent path is created for each datagram

Virtual circuit switching A route is created from source to destination

before transmission begins and all datagrams are sent using the same route


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Networks vs. Clusters

Externally, clusters appear as a single computing unit.

Network nodes are individually identifiable.

Workload on a cluster is determined by cluster administration and load-balancing software.

Network workload cannot be controlled using the above method.


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High Performance Computing

Massively parallel processor architectures (MPP)

Clusters of power machines or larger Beowulf blade clusters Well suited for problems that can be broken into

subtasks

Grid computing Supercomputer performance through distributing

CPU processing to the spare CPU cycles of personal computers connected to a network


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Parallel Computers

Massively parallel architectures Hundreds to millions of CPUs CPUs have small amounts of local memory All CPUs have access to global shared

memory Pipelined CPUs

Results from one CPU flow to the next CPU for additional processing

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Chapter 11 Modern Computer Systems, Clusters, and Networks