Discuss in detail SISD, SIMD, MISD, MIMD, SIMT, SPMD, MPMD.

Q. Discuss in detail SISD, SIMD, MISD, MIMD, SIMT, SPMD, MPMD. (MAY 19) 10M

Q. Explain SIMD, MIMD, SIMT. (DEC 18) 10M

Ans- 1. Single-instruction, single-data (SISD) –

A SISD computing system is a uniprocessor machine which is capable of executing a single instruction, operating on a single data stream. In SISD, machine instructions are processed in a sequential manner and computers adopting this model are popularly called sequential computers. Most conventional computers have SISD architecture. All the instructions and data to be processed have to be stored in primary memory. The speed of the processing element in the SISD model is limited(dependent) by the rate at which the computer can transfer information internally. Dominant representative SISD systems are IBM PC, workstations.

2. Single-instruction, multiple-data (SIMD) –

A SIMD system is a multiprocessor machine capable of executing the same instruction on all the CPUs but operating on different data streams. Machines based on a SIMD model are well suited to scientific computing since they involve lots of vector and matrix operations. So that the information can be passed to all the processing elements (PEs) organized data elements of vectors can be divided into multiple sets (N-sets for N PE systems) and each PE can process one data set. Dominant representative SIMD systems is Cray’s vector processing machine.

3. Multiple-instruction, single-data (MISD) –

A MISD computing system is a multiprocessor machine capable of executing different instructions on different PEs but all of them operating on the same dataset.

Example Z = sin(x)+cos(x)+tan(x)

The system performs different operations on the same data set. Machines built using the MISD model are not useful in most of the application, a few machines are built, but none of them are available commercially.

4. Multiple-instruction, multiple-data (MIMD) –

A MIMD system is a multiprocessor machine which is capable of executing multiple instructions on multiple data sets. Each PE in the MIMD model has separate instruction and data streams; therefore, machines built using this model are capable to any kind of application. Unlike SIMD and MISD machines, PEs in MIMD machines work asynchronously. MIMD machines are broadly categorized into shared-memory MIMD and distributed-memory MIMD based on the way PEs are coupled to the main memory.

5. Single-instruction, multiple-data (SIMD) –

A SIMT is an execution model used in parallel computing where single-instruction, multiple data is combined with multithreading. The processors, say a number p of them, seem to execute many more than p tasks. This is achieved by each processor having multiple threads, which execute in lock-step, and are analogous to SIMD lanes. The SIMT execution model has been implemented on several GPUs and is relevant for general-purpose computing on graphics processing units (GPGPU), e.g. some supercomputers combine CPUs with GPUs. SIMT was introduced by Nvidia.

6. Single-program, multiple-data (SIMD) –

SPMD is actually a “high level” programming model that can be built upon any combination of the previously mentioned parallel programming models. A single program is executed by all tasks simultaneously. At any moment of time, tasks can be executing the same or different instructions within the same program. SPMD programs usually have the necessary logic programmed into them to allow different tasks to branch or conditionally execute only those parts of the program they are designed to execute. That is, tasks do not necessarily have to execute the entire program – perhaps only a portion of it. All tasks may use different data.

7. Multiple-program, multiple-data (SIMD) –

Like SPMD, MPMD is actually a “high level” programming model that can be built upon any combination of the previously mentioned parallel programming models. MPMD applications typically have multiple executable object files (programs). While the application is being run in parallel, each task can be executing the same or different program as other tasks. All tasks may use different data.