05-04-2012, 04:05 PM
Distributed Systems
DIS. SYS..ppt (Size: 51 KB / Downloads: 259)
Advantages of Distributed Systems over Centralized Systems
Economics: a collection of microprocessors offer a better price/performance than mainframes. Low price/performance ratio: cost effective way to increase computing power.
Speed: a distributed system may have more total computing power than a mainframe. Ex. 10,000 CPU chips, each running at 50 MIPS. Not possible to build 500,000 MIPS single processor since it would require 0.002 nsec instruction cycle. Enhanced performance through load distributing.
Inherent distribution: Some applications are inherently distributed. Ex. a supermarket chain.
Reliability: If one machine crashes, the system as a whole can still survive. Higher availability and improved reliability.
Incremental growth: Computing power can be added in small increments. Modular expandability
Another deriving force: the existence of large number of personal computers, the need for people to collaborate and share information.
Hardware Concepts
MIMD (Multiple-Instruction Multiple-Data)
Tightly Coupled versus Loosely Coupled
Tightly coupled systems (multiprocessors)
shared memory
intermachine delay short, data rate high
Loosely coupled systems (multicomputers)
private memory
intermachine delay long, data rate low
Multicomputers
Bus-Based Multicomputers (Fig. 9-7)
easy to build
communication volume much smaller
relatively slow speed LAN (10-100 MIPS, compared to 300 MIPS and up for a backplane bus)
Switched Multicomputers (Fig. 9-8)
interconnection networks: E.g., grid, hypercube
hypercube: n-dimensional cube
Types of transparency
Location Transparency: users cannot tell where hardware and software resources such as CPUs, printers, files, data bases are located.
Migration Transparency: resources must be free to move from one location to another without their names changed.E.g., /usr/lee, /central/usr/lee
Replication Transparency: OS can make additional copies of files and resources without users noticing.
Concurrency Transparency: The users are not aware of the existence of other users. Need to allow multiple users to concurrently access the same resource. Lock and unlock for mutual exclusion.
Parallelism Transparency: Automatic use of parallelism without having to program explicitly. The holy grail for distributed and parallel system designers.
Users do not always want complete transparency: a fancy printer 1000 miles away
Communication Networks
Computers are connected through a communication network
Wide Area Networks (WAN)connect computers spread over a wide geographic areapoint-to-point or store-and-forward -- data is transferred between computers through a series of switchesswitch -- a special purpose computer responsible for routing data (to avoid network congestion)data can be lost due to: switch crashes, communication link failures, limited buffers at switches, transmission errors, etc.
DIS. SYS..ppt (Size: 51 KB / Downloads: 259)
Advantages of Distributed Systems over Centralized Systems
Economics: a collection of microprocessors offer a better price/performance than mainframes. Low price/performance ratio: cost effective way to increase computing power.
Speed: a distributed system may have more total computing power than a mainframe. Ex. 10,000 CPU chips, each running at 50 MIPS. Not possible to build 500,000 MIPS single processor since it would require 0.002 nsec instruction cycle. Enhanced performance through load distributing.
Inherent distribution: Some applications are inherently distributed. Ex. a supermarket chain.
Reliability: If one machine crashes, the system as a whole can still survive. Higher availability and improved reliability.
Incremental growth: Computing power can be added in small increments. Modular expandability
Another deriving force: the existence of large number of personal computers, the need for people to collaborate and share information.
Hardware Concepts
MIMD (Multiple-Instruction Multiple-Data)
Tightly Coupled versus Loosely Coupled
Tightly coupled systems (multiprocessors)
shared memory
intermachine delay short, data rate high
Loosely coupled systems (multicomputers)
private memory
intermachine delay long, data rate low
Multicomputers
Bus-Based Multicomputers (Fig. 9-7)
easy to build
communication volume much smaller
relatively slow speed LAN (10-100 MIPS, compared to 300 MIPS and up for a backplane bus)
Switched Multicomputers (Fig. 9-8)
interconnection networks: E.g., grid, hypercube
hypercube: n-dimensional cube
Types of transparency
Location Transparency: users cannot tell where hardware and software resources such as CPUs, printers, files, data bases are located.
Migration Transparency: resources must be free to move from one location to another without their names changed.E.g., /usr/lee, /central/usr/lee
Replication Transparency: OS can make additional copies of files and resources without users noticing.
Concurrency Transparency: The users are not aware of the existence of other users. Need to allow multiple users to concurrently access the same resource. Lock and unlock for mutual exclusion.
Parallelism Transparency: Automatic use of parallelism without having to program explicitly. The holy grail for distributed and parallel system designers.
Users do not always want complete transparency: a fancy printer 1000 miles away
Communication Networks
Computers are connected through a communication network
Wide Area Networks (WAN)connect computers spread over a wide geographic areapoint-to-point or store-and-forward -- data is transferred between computers through a series of switchesswitch -- a special purpose computer responsible for routing data (to avoid network congestion)data can be lost due to: switch crashes, communication link failures, limited buffers at switches, transmission errors, etc.