Chapter 11

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

Mainframe Computer System

Major PC System Components

System Performance Improvements

 Multiple CPUs

 Faster clock speed, buses and circuits

 Wider instruction and data paths

 Faster disk access

 More and faster memory

Multiprocessing

 Reasons

 Increase the processing power of a system

 Parallel processing

 Types of multiprocessor systems

 Tightly coupled systems

 Loosely coupled systems

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)

Tightly Coupled Systems

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

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

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

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

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)

Cluster Models

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

Blade and Rack of Beowulf Cluster

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

Example: Point-to-Point

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

Client-Server Network

LAN Topology

 Arrangement of workstations in a shared medium environment

 Logical arrangement (data flow)

 Physical arrangement (cabling scheme)

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

Bus LAN Diagram

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

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

Ring LAN Diagram

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

Star LAN Diagram

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

Ethernet Frame

Switched Ethernet

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

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.

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

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

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

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.

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

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

Copyright 2003 John Wiley & Sons

All rights reserved. Reproduction or translation of this work beyond that permitted in Section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the permissions Department, John Wiley & Songs, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publisher assumes no responsibility for errors, omissions, or damages caused by the use of these programs or from the use of the

information contained herein.”