MIMD machines

MIMD Multicomputers. Probably the most widely available parallel computers are the shared-memory multiprocessor MIMD machines. Examples include the multiprocessor vector supercomputers, IBM mainframes, VAX minicomputers. Convex and AUiant rninisupercomputers, and SiUcon... 

The Advanced Flexible Processor is a unique entry into the multiprocessing field. It provides the dynamic capabilities offered by an MIMD machine with advanced features provided by the interprocessor ring communications network efficient utilization of the system processors is therefore effected. Within each Advanced Flexible Processor, dynamic multiple chaining can be achieved due to the superior flexibility of the... 

The Thinking Machines Corporation (TMC) CM5 MPP system was announced in November 1991. This processor is a distributed-memory MIMD machine that supports both the SIMD and MIMD programming models. The hardware is composed of a fat tree of compute processors that are used and administered from control processors. The compute processing nodes consist... 

B. R. Brooks and M. Hodoscek, Chem. Design Autom. News, 7, 16 (1992). Parallelization of CHARMM for MIMD Machines. 

R. K, Kalia, S. De Leeuw, A., Nakano, and P. Vashishta, Comput. Phys. Commun., 74, 316 (1993). Molecular-Dynamics Simulations of Coulombic Systems on Distributed-Memory MIMD Machines. 

The multiple-instruction, multiple-data (MIMD) architecture permits multiple instruction streams to simultaneously interact with their own data stream. While MIMD machines composed of completely independent pairs of instruction and data streams may be of use for trivially parallel applications, it is generally necessary to use a network to connect the processors together in a way that allows a given processor s data stream to be supplemented by... 

Each of the individual nodes discussed in the previous section can be a MIMD parallel computer. Larger MIMD machines can be constructed by connecting many MIMD nodes via a high-performance network. While each node can have shared memory, memory is typically not shared between the nodes, at least not at the hardware level. Such machines are referred to as distributed memory computers or clusters, and in this section we consider such parallel computers in more detail. 

The memory hierarchy in a hypothetical MIMD machine constructed from the nodes in Figure 2.15 and the network in Figure 2.12. Logically equivalent data location types are subdivided by how many network hops are needed to reach them, Whop (intra-node hops for local memory, inter-node hops for remote memory). The estimate of the time required to access memory at the given location is access (this time is hypothetical and not based on any particular hardware). The level of treatment typically used for each memory level is given for the several layers of software... 

There are many types of possible computer architecture, including parallel architectures [1, 2]. However, by far the most common one for simulators is the so-called MIMD architecture (multiple instruction stream - multiple data stream). On MIMD machines, each processing element is able to act independently (unlike some other specialist parallel machines). This provides maximum flexibility to the programmer, and unsurprisingly MIMD machines make up most of todays parallel systems. 

DM-MIMD MPP machines are undoubtedly the fastest-growing class in the family of supercomputers, although this type of machine is more difficult to deal with than shared-memory machines and processor-array machines. For shared-memory systems the data distribution is completely transparent to the user. This is quite different for DM-MIMD systems, where the user has to distribute the data over the processors, and also the data exchange between processors has to be performed explicitly. The initial reluctance to use DM-MIMD machines has decreased lately. This is partly due to the now-existing standards for communication software such as MPI (message passing interface) and PVM (parallel virtual machine) and is partly because, at least theoretically, this class of systems is able to outperform all other types of machines. 

DM-MIMD systems have several advantages the bandwidth problem that haunts shared-memory systems is avoided because the bandwidth scales up automatically with the number of processors. Furthermore, the speed of the memory, which is another critical issue with shared-memory systems (to get a peak performance that is comparable to that of DM-MIMD systems, the processors of shared-memory machines should be very fast and the speed of the memory should match it), is less important for DM-MIMD machines because more processors can be configured without the aforementioned bandwidth problems. 

Some vendors have included hardware assistence such that all of the processors can access all of the address space. Therefore, such systems can be considered SM-MIMD machines. On the other hand, because the memory is physically distributed, it cannot be guaranteed that a... 

For all practical purposes we can classify these systems as SM-MIMD machines also because special assisting hardware/software (such as a directory memory) has been incorporated to establish a single system image, although the memory is physically distributed. 

MIMD-based computers employ independent processors running different programming instructions concurrently and working on different data. There are a number of different ways to construct MIMD machines, according to the relationship of processors to memory and to the topology of the processors. 

---