Uniform memory access

As noted above, one of the goals of NAMD 2 is to take advantage of clusters of symmetric multiprocessor workstations and other non-uniform memory access platforms. This can be achieved in the current design by allowing multiple compute objects to run concurrently on different processors via kernel-level threads. Because compute objects interact in a controlled manner with patches, access controls need only be applied to a small number of structures such as force and energy accumulators. A shared memory environment will therefore contribute almost no parallel overhead and generate communication equal to that of a single-processor node. 

CC — NUMA Cache Coherent Non-Uniform Memory Access-machines... 

NUMA Non-Uniform Memory Access-machines NV Normalized Variable ODE Ordinary Differential Equations PEE Population Balance Equation... 

Shared memory computers in which all processors have equal access to all memory in the system are referred to as symmetric multiprocessors (SMP), and may also be called uniform memory access (UMA) computers. In the node shown in Figure 2.15, references to memory may need to pass through one, two, or three crossbar switches, depending on where the referenced memory is located. Thus, this node technically has a nonuniform memory access (NUMA) architecture, and, since the node is cache-coherent, this architecture is called ccNUMA. However, since the crossbar switches in the quad-core AMD Opteron implementation of ccNUMA exhibit high performance, this particular node would typically be considered to be an SMP. 

Virtual machines also serve as the unit of fault contaimnent. Hardware or software faults only affect the virtual machines that actually used the faulty resource. Disco also handles memory management issues that arise from non-uniform memory access by transparently doing page replication and migration. Again, changing commodity operating systems to do this would be more diffi-... 

Installing extra off-chip main memory The stacked DRAM and off-chip DRAM have different access delays and thus this approach implies a Non-Uniform Memory Architecture (NIJMA)1231. The operating system has to take charge of the resultant memory management issues. 

Some comments on the problem of PC modulation should be made here. Using this technique, the digitized signal is usually modulated in a pure bineu y code, represented as a data term (byte), that is, a bit pattern composed of a series of uniform impulses and spaces ( T and 0 ). Finally, the coded data are stored. For short-term storage, RAM memory chips and other semiconductor memories are used, which have access times from hundreds of nanoseconds to 1 microsecond. In contrast, access times for secondary long-term memories, e. g. magnetic discs, floppy discs, cassette recorders... 

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