1. Hardware/Software Concepts Tran, Van Hoai Department of Systems & Networking Faculty of Computer Science & Engineering HCMC University of Technology

2. Hardware concepts Multiprocessor dimensions – Memory: could be shared or be private to each CPU – Interconnect: could be shared (bus-based) or switched MMM PPPP PPPP MMMM MMM PPPP PPPP MMMM

3. Computer hardware models (1) Bus-based multiprocessor Homogeneous Multicomputer Systems Grid Hypercube MPP (massively parallel processor) COW (Cluster of workstations)

4. Computer hardware models (2) Heterogenous Multicomputer Systems – Different systems processor type memory size IO bandwidth – No global system view for application performance and service not guaranteed the same everywhere Need a software to provide transparency to applications

5. Software concepts Distributed systems similar to traditional OS – managing resources such a CPU, memory, peripheral devices, network, data, etc. – allowing multiple users, applications OS for distributed systems classified into – Tightly-coupled: distributed OS (DOS) for multiprocessor, homogeneous multicomputer – Loosly-coupled: network OS (NOS) for heterogeneous multicomputer Middleware needed to provide better distribution transparency

6. Uniprocessor OS (1) Structure of uniprocessor operating systems – Monolithic (e.g., MS-DOS, early UNIX, Windows) One large kernel that handles everything – Layered design Functionality is decomposed into N layers Each layer uses services of layer N-1 and implements new service(s) for layer N+1

7. Uniprocessor OS (2) Microkernel architecture Small kernel User-level servers implement additional functionality

8. Multiprocessor OS Protect against concurrent access to single memory by multiple processors Most of OSs have been redesigned from the start to handle multiple processors

9. Multicomputer OS No single memory space – more complex in structure of OS Machine A Kernel Machine B Kernel Machine C Kernel Distributed applications Distributed OS service Provides Virtual multiprocess or machine Message passing service

10. Distributed shared memory (1) CPU1CPU2CPU4CPU3 0 25 9 136 8 4711 12 1315 1410 12 0 3456789 1112131415

11. Distributed shared memory (2) CPU1CPU2CPU4CPU3 0 25 9 136 8 4711 12 1315 1410 12 0 3456789 1112131415 After a reference of CPU1 to memory 10

12. Distributed shared memory (3) CPU1CPU2CPU4CPU3 0 25 9 136 8 4711 12 1315 1410 12 0 3456789 1112131415 After a read-only reference of CPU1 to memory 10 10 Tradeoff between efficiency and programmability

13. Network OS NOS provides facilities to allow users to make use of the services available on specific machine Machine A Kernel Machine B Kernel Machine C Kernel Distributed applications Network OS service

14. Why middleware needed ? DOS, NOS not yet qualify strict definition of a distributed system need a middleware for NOS in order to achieve scalability and openness of NOS transparency and easy-to-use of DOS

15. Where to place middleware ? Machine A Kernel Machine B Kernel Machine C Kernel Distributed applications Network OS service Middleware services Network

16. Middleware models Everything as a file – keyboard, mouse, disk, network interface, etc. Distributed file system Remote Procedure Call (RPC) Distributed object

17. Middleware issues Middleware services – high-level communication service to provide access transparency – naming service to allow entities to be shared and looked up (as in directory) – Storage – Security

18. Openness Machine A Same programming interface Machine C Network OS service Middleware Network Middleware application common protocol

19. Comparison between systems ItemDistributed OSNetwork OSMiddleware -based OS Multiproc.Multicomp. Degree of transparencyvery highHighLowHigh Same OS on all nodes?Yes No Number of copies of OS1NNN Basis for communicationShared memory MessagesFilesModel specific Resource managementGlobal, central Global, distributed Per node ScalabilityNoModeratelyYesVarifies OpennessClosed Open

20. Homeworks Read section 1.5 “The client – server model” in reference 1 (Tanenbaum) To understand – Why need the client-server model ? – Client-server architectures ?