Difference Between SIMD and MIMD

SIMD and MIMD are types of computer architectures that are used to improve the performance of certain types of computational tasks. The basis of this classification is the number of data and instruction streams. SIMD, short for Single Instruction Multiple Data, computer architecture can execute a single instruction on multiple data streams. On the other hand, the MIMD (Multiple Instruction Multiple Data) computer architectures can execute several instructions on multiple data streams.

Read this article to find out more about SIMD and MIMD architectures and how they are different from each other.

What is SIMD?

SIMD is a form of parallel computer architecture that is categorized under Flynn’s classification given by Michael Flynn. In the SIMD architecture, a single instruction is applied to several data streams. SIMD consists of a single control signal that is used to call several isolated processing units. Therefore, all the processing units accept the same instruction from the control unit and use it on separate elements of data.

The SIMD organization uses shared memory unit which is divided into different modules. As a result, the memory unit can interact with all the processing units simultaneously. Since the SIMD architecture uses a single copy of instruction on multiple data streams, it requires less memory. Also, SIMD requires a single instruction decoder which reduces the overall cost of the system.

SIMD architectures are particularly effective for tasks that can be easily parallelized, such as image processing, video encoding and decoding, etc.

What is MIMD?

The MIMD architecture consists of multiple instructions and data streams. Therefore, MIMD architecture requires multiple processing units. For this reason, MIMD systems are considered to have most complex organization, but they are highly efficient.

The MIMD architecture uses several instructions over different data streams simultaneously. This provides high concurrency. The MIMD system can work with shared and distributed memory model efficiently.

The MIMD architecture does not need any additional control unit which reduces the cost of the system. It also provides efficient execution of the conditional statements such as if/else statements. This is because the processing unit is independent.

MIMD architectures are more flexible and are better suited for tasks that require more complex and varied computation, such as general−purpose computing and AI applications.

Difference between SIMD and MIMD

The following table highlights the important differences between SIMD and MIMD:

S. No.	SIMD	MIMD
1.	SIMD stands for Single Instruction Multiple Data.	MIMD stands for Multiple Instruction Multiple Data.
2.	It requires less memory.	It requires more memory.
3.	It is inexpensive in comparison to MIMD.	It is expensive in comparison to SIMD.
4.	It has a single decoder.	It contains multiple decoders.
5.	It uses latent (tacit) synchronization.	It uses accurate (explicit) synchronization.
6.	It is a synchronous programming technique.	It is an asynchronous programming technique.
7.	It is simple in comparison to MIMD.	It is complex in comparison to SIMD.
8.	It is not as efficient as MIMD in terms of performance.	It is efficient in comparison to SIMD.

Conclusion

SIMD allows synchronous processing where a single instruction is carried out on multiple data streams at the same time, whereas the MIMD architecture follows the asynchronous mechanism where multiple instructions operate on multiple data streams. The SIMD architecture is less complex as compared to the MIMD architecture.

In general, both SIMD and MIMD architectures can be useful for improving the performance of certain types of computational tasks. SIMD architectures provide more parallelism but they are less flexible, while MIMD architectures provide more flexibility with less parallelism.