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 Wilson Wong, Bentley College Linda Senne, Bentley College

Basic Personal Computer System Chapter 11: Modern Computer Systems, Clusters, and Networks

Mainframe Computer System Chapter 11: Modern Computer Systems, Clusters, and Networks

Major PC System Components Chapter 11: Modern Computer Systems, Clusters, and Networks

System Performance Improvements Multiple CPUs Faster clock speed, buses and circuits Wider instruction and data paths Faster disk access More and faster memory Chapter 11: Modern Computer Systems, Clusters, and Networks

Multiprocessing Reasons Types of multiprocessor systems Increase the processing power of a system Parallel processing Types of multiprocessor systems Tightly coupled systems Loosely coupled systems Chapter 11: Modern Computer Systems, Clusters, and Networks

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) Chapter 11: Modern Computer Systems, Clusters, and Networks

Tightly Coupled Systems Chapter 11: Modern Computer Systems, Clusters, and Networks

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 Chapter 11: Modern Computer Systems, Clusters, and Networks

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 Chapter 11: Modern Computer Systems, Clusters, and Networks

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 Chapter 11: Modern Computer Systems, Clusters, and Networks

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 Chapter 11: Modern Computer Systems, Clusters, and Networks

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) Chapter 11: Modern Computer Systems, Clusters, and Networks

Cluster Models Chapter 11: Modern Computer Systems, Clusters, and Networks

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 Chapter 11: Modern Computer Systems, Clusters, and Networks

Blade and Rack of Beowulf Cluster Figure 11.9 Chapter 11: Modern Computer Systems, Clusters, and Networks

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 Chapter 11: Modern Computer Systems, Clusters, and Networks

Example: Point-to-Point Chapter 11: Modern Computer Systems, Clusters, and Networks

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 Chapter 11: Modern Computer Systems, Clusters, and Networks

Client-Server Network Chapter 11: Modern Computer Systems, Clusters, and Networks

LAN Topology Arrangement of workstations in a shared medium environment Logical arrangement (data flow) Physical arrangement (cabling scheme) Chapter 11: Modern Computer Systems, Clusters, and Networks

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 Chapter 11: Modern Computer Systems, Clusters, and Networks

Bus LAN Diagram Chapter 11: Modern Computer Systems, Clusters, and Networks

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 Chapter 11: Modern Computer Systems, Clusters, and Networks

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 Chapter 11: Modern Computer Systems, Clusters, and Networks

Ring LAN Diagram Chapter 11: Modern Computer Systems, Clusters, and Networks

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 Chapter 11: Modern Computer Systems, Clusters, and Networks

Star LAN Diagram Chapter 11: Modern Computer Systems, Clusters, and Networks

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 Chapter 11: Modern Computer Systems, Clusters, and Networks

Ethernet Frame Chapter 11: Modern Computer Systems, Clusters, and Networks

Switched Ethernet Chapter 11: Modern Computer Systems, Clusters, and Networks

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 Chapter 11: Modern Computer Systems, Clusters, and Networks

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. Chapter 11: Modern Computer Systems, Clusters, and Networks

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 Chapter 11: Modern Computer Systems, Clusters, and Networks

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 Chapter 11: Modern Computer Systems, Clusters, and Networks

Wide Area Network Circuit switching Message switching Packet 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 Chapter 11: Modern Computer Systems, Clusters, and Networks

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. Chapter 11: Modern Computer Systems, Clusters, and Networks

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 Chapter 11: Modern Computer Systems, Clusters, and Networks

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 Chapter 11: Modern Computer Systems, Clusters, and Networks

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