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
Wilson Wong, Bentley College
Linda Senne, Bentley College
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Basic Personal Computer System
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Mainframe Computer System
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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
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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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Copyright 2003 John Wiley & Sons
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