1. UNIT-I

2. 11/14/00CSE 3802 UNIT-I Distributed Systems ECS-701 Lecture Note NEERAJ KUMAR

3. 3 What is a Distributed System?  Tanenbaum and van Renesse: A distributed system is one that looks to its users like an ordinary, centralized, system but runs on multiple independent CPUs  Symptoms? Shroeder:  Multiple, independent processing units  Processors communicate via a hardware interconnect  Processing unit failures are independent  Manage resource sharing  State is shared among processors Distributed Systems

4. 4 Design Issues  Scaling  Communication  Coordination  Transparency  Naming  Load sharing  Consistency  Failures  Security  Heterogeneity  Mobility Distributed Systems, cont.

5. 11/14/00CSE 3805 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.

6. 11/14/00CSE 3806 Advantages of Distributed Systems over Independent PCs – Data sharing: allow many users to access to a common data base – Resource Sharing: expensive peripherals like color printers – Communication: enhance human-to-human communication, e.g., email, chat – Flexibility: spread the workload over the available machines

7. 11/14/00CSE 3807 Disadvantages of Distributed Systems – Software: difficult to develop software for distributed systems – Network: saturation, lossy transmissions – Security: easy access also applies to secrete data

8. Algorithms One processor –Reliable (no faults) –No communication Sequential : –One step at a time Complexity : –Step complexity Examples : –Sorting (Quicksort, Mergesort, Heapsort) –Searching (Binary search) –Matrix mult. (Strassen’s) –Primality testing Distributed kdAlgorithms  Many processors –Faulty (crash, byzantine, etc.) –Communication over network  Concurrent : –One step at a time  Complexity : –Message complexity –Latency analysis  Examples : –Leader election –Consensus (Agreement) –Mutual exclusion (Dining Philosophers) –Atomic objects