● DSM is a term in computer science that refers to a wide class of
software and hardware implementations, in which each node of a cluster
has access to shared memory in addition to each node's non-shared
●Distributed Shared Memory (DSM), also known as a distributed global
address space (DGAS).
●The processors communicate with one another through various
communication networks,such as high-speed buses or telephone lines.
●A distributed system is a collection of loosely coupled processors
interconnected by a communication network.
There are four major advantage of distributed
1. Resource Sharing
2. Computation Speedup
General Architecture of Distributed Shared
Memory (DSM) System :
●It consists of number of nodes or machines or
computer each of which is connected to each other
through high speed communication channel. Each
node has several components associated with it.
●A software memory mapping manager of each node
maps its local memory into the memory mapping into
the virtual shared memory. We call it the Distributed
Algorithims of DSM
The algorithims for implementing DSM deal
with two basic problems
➔ Static and Dynamic distribution of shared data
across the system, to minimize access latency,
➔Preserving a coherent view of shared data ,while
minimizing coherence-management overhead.
Design and Implementation Issues
Thee are various factors that have to be kept In mind while
designing and implementing the DSM systems. They are as
As we know, transfer of the memory blocks is the
major operation in the DSM systems. Therefore block size matters a
Size of the block depends on various factors like, paging overhead,
thrashing, false sharing, and directory size.
It may happen that one node might be accessing for a memory block
from DSM when its own local memory is completely full. In such a
case, when the memory block migrating from remote node reaches, it
finds no space to get placed. Thus a replacement strategy of major
concern in the design and implementation of the DSM systems.
Certain block must be removed so as to place the new blocks in such
a situation. Several techniques are used for the replacement of old
blocks such as removal of Least Recently Used memory blocks.
2.Structure of Shared Memory Space
How the shared memory space is organized with data determines the
structure of the shared memory space. It refers to the layout of shared
data. It depends upon the type of application the DSM is going to