Chapter 11
Modern 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
Basic Personal Computer System
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Mainframe Computer System
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Systems, Clusters, and Networks
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Major PC System Components
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System Performance
Improvements
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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-topoint 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
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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 loadbalancing 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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Systems, Clusters, and Networks
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Parallel Computers
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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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