Distributed shred memory architecture

distributed Shared memory

1. DSM architecture, advantages & disadvantages Subject: DOS CE-B Maulik togadiya 130240107090 Guided by: Nirav shah

2. What is shared memory? On-Chip Memory CPU Memory CPU1 Memory CPU4 CPU2 CPU3 Chip package Address and data lines Connecting the CPU to the memory extension A single-chip computer A hypothetical shared-memory Multiprocessor.

3. Introduction D istributed shared memory  ( DSM ) is a form of memory architecture where the (physically separate) memories can be addressed as one (logically shared) address space. Here, the term "shared" does not mean that there is a single centralized memory but "shared" means that the address space is shared. The shared memory model provides a virtual address space shared between all nodes. The overcome the high cost of communication in distributed systems, DSM systems move data to the location of access.

4. How it works? Data moves between main memory and secondary memory (within a node) and between main memories of different nodes. When a process accesses data in the shared address space, the mapping manager maps shared memory address to physical memory (local or remote ).

5. DSM architecture High speed communication network is used for connecting nodes. A simple message passing system allows on different node to exchange message with each other. Memory mapping manager routine in each node maps local memory onto the shared virtual memory. For mapping operation, the shared memory space is partitioned into blocks. The main memory of individual nodes is used to cache of shared memory space.

6. Memory Mapping Manager Memory Mapping Manager Memory Mapping Manager Shared Memory NODE 1 NODE 2 NODE 3 Communication network

7. Systems that support DSM,data moves between secondary memory and main memory as well as between main memories of different nodes. When process access data in shared address space, a mapping manager maps the shared memory address to the physical memory. The mapping manager is layer of software implemented either in the operating kernel or as runtime library routine. DSM architecture

8. Advantages Shields programmer from send/receive primitives. DSM is usually cheaper than using multiprocessor system. DSM provides large virtual memory space. DSM programs portable as they use common DSM programming interface. It can handle complex and large data bases without replication or sending the data to processes. No memory access bottleneck.

9. Disadvantages Must provide for protection against simultaneous access to shared data such as lock.. It could cause a performance penalty. Little programmer control over actual messages being generated. Performance of irregular problems could be difficult. Programmers need to be understand consistency model to write correct programs.