Difference between Shared Memory Model and Message Passing Model in IPC

Prerequisite – Inter-Process Communication

1. Shared Memory Model:
In this IPC model, a shared memory region is established which is used by the processes for data communication. This memory region is present in the address space of the process which creates the shared memory segment. The processes that want to communicate with this process should attach this memory segment into their address space. 

2. Message Passing Model:
In this model, the processes communicate with each other by exchanging messages. For this purpose, a communication link must exist between the processes and it must facilitate at least two operations send (message) and receive (message). The size of messages may be variable or fixed. 

Difference between Shared Memory Model and Message Passing Model in IPC :

S.No	Shared Memory Model	Message Passing Model
1.	The shared memory region is used for communication.	A message passing facility is used for communication.
2.	It is used for communication between processes on a single processor or multiprocessor systems where the communicating processes reside on the same machine as the communicating processes share a common address space.	It is typically used in a distributed environment where communicating processes reside on remote machines connected through a network.
3.	The code for reading and writing the data from the shared memory should be written explicitly by the Application programmer.	No such code required here as the message passing facility provides mechanism for communication and synchronization of actions performed by the communicating processes.
4.	It provides a maximum speed of computation as communication is done through shared memory so system calls are made only to establish the shared memory.	It is time-consuming as message passing is implemented through kernel intervention (system calls).
5.	Here the processes need to ensure that they are not writing to the same location simultaneously.	It is useful for sharing small amounts of data as conflicts need not to be resolved.
6.	Faster communication strategy.	Relatively slower communication strategy.
7.	No kernel intervention.	It involves kernel intervention.
8.	It can be used in exchanging larger amounts of data.	It can be used in exchanging small amounts of data.
9.	Example-  Data from a client process may need to be transferred to a server process for modification before being returned to the client.	Example-  Web browsers Web Servers Chat program on WWW (World Wide Web)