Static random-access memory is a type of semiconductor memory that uses bistable latching circuitry (flip-flop) to store each bit. SRAM exhibits data remanence, but it is still volatile in the conventional sense that data is eventually lost when the memory is not powered.
Hidden Markov Model (HMM) is a statistical Markov model in which the system being modeled is assumed to be a Markov process with unobservable states.
The Scalable Coherent Interface or Scalable Coherent Interconnect (SCI), was a high-speed interconnect standard for shared memory multiprocessing and message passing used in the 1990s. The goal was to scale well, provide system-wide memory coherence and a simple interface; i.e. a standard to replace buses in multiprocessor systems without the inherent scalability and performance limitations of buses. The IEEE Std 1596-1992, IEEE Standard for Scalable Coherent Interface (SCI) was approved by the IEEE standards board on March 19, 1992.
In computer architecture, cache coherence is the uniformity of shared resource data that ends up stored in multiple local caches. When clients in a system maintain caches of a common memory resource, problems may arise with incoherent data, which is particularly the case with CPUs in a multiprocessing system.
Bus snooping or bus sniffing is a scheme by which a coherency controller (snooper) in a cache monitors or snoops the bus transactions, and its goal is to maintain a cache coherency in distributed shared memory systems. A cache containing a coherency controller (snooper) is called a snoopy cache. This scheme was introduced by Ravishankar and Goodman in 1983.
In computer science, distributed shared memory (DSM) is a form of memory architecture where physically separated memories can be addressed as one logically shared address space. Here, the term "shared" does not mean that there is a single centralized memory, but that the address space is "shared". Distributed global address space (DGAS), is a similar term for a wide class of software and hardware implementations, in which each node of a cluster has access to shared memory in addition to each node's non-shared private memory.
In computing, the MSI protocol - a basic cache-coherence protocol - operates in multiprocessor systems. As with other cache coherency protocols, the letters of the protocol name identify the possible states in which a cache line can be.
The MOSI protocol is an extension of the basic MSI cache coherency protocol. It adds the Owned state, which indicates that the current processor owns this block, and will service requests from other processors for the block.
In computing, MOESI is a full cache coherency protocol that encompasses all of the possible states commonly used in other protocols. In addition to the four common MESI protocol states, there is a fifth "Owned" state representing data that is both modified and shared. This avoids the need to write modified data back to main memory before sharing it. While the data must still be written back eventually, the write-back may be deferred.
IEEE 802.11r-2008 or fast BSS transition (FT), also called fast roaming, is an amendment to the IEEE 802.11 standard to permit continuous connectivity aboard wireless devices in motion, with fast and secure handoffs from one base station to another managed in a seamless manner. It was published on July 15, 2008. IEEE 802.11r-2008 was rolled up into 802.11-2012.
The Intel 82497 is a Cache Controller for the P5 Pentium processor. It works with multiple 82492 Cache SRAMs.
In cache coherency protocol literature, Write-Once was the first MESI protocol defined. It has the optimization of executing write-through on the first write and a write-back on all subsequent writes, reducing the overall bus traffic in consecutive writes to the computer memory. It was first described by James R. Goodman in (1983). Cache coherence protocols are an important issue in Symmetric multiprocessing systems, where each CPU maintains a cache of the memory.
The Firefly cache coherence protocol is the schema used in the DEC Firefly multiprocessor workstation, developed by DEC Systems Research Center. This protocol is a 3 State Write Update Cache Coherence Protocol. Unlike the Dragon protocol, the Firefly protocol updates the Main Memory as well as the Local caches on Write Update Bus Transition. Thus the Shared Clean and Shared Modified States present in case of Dragon Protocol, are not distinguished between in case of Firefly Protocol.
The Dragon Protocol is an update based cache coherence protocol used in multi-processor systems. Write propagation is performed by directly updating all the cached values across multiple processors. Update based protocols such as the Dragon protocol perform efficiently when a write to a cache block is followed by several reads made by other processors, since the updated cache block is readily available across caches associated with all the processors.
The MESIF protocol is a cache coherency and memory coherence protocol developed by Intel for cache coherent non-uniform memory architectures. The protocol consists of five states, Modified (M), Exclusive (E), Shared (S), Invalid (I) and Forward (F).
Espresso is the codename of the 32-bit central processing unit (CPU) used in Nintendo's Wii U video game console. It was designed by IBM, and was produced using a 45 nm silicon-on-insulator process. The Espresso chip resides together with a GPU from AMD on a MCM manufactured by Renesas. It was revealed at E3 2011 in June 2011 and released in November 2012.
The CPU cache is a piece of hardware which reduces the access time to the data in the memory by keeping some part of the frequently used data of the main memory in itself. It is smaller and faster than the main memory.
Directory-based coherence is a mechanism to handle Cache coherence problem in Distributed shared memory (DSM) a.k.a. Non-Uniform Memory Access (NUMA). Another popular way is to use a special type of computer bus between all the nodes as a "shared bus". Directory-based coherence uses a special directory to serve instead of the shared bus in the bus-based coherence protocols. Both of these designs use the corresponding medium as tool to facilitate the communication between different nodes, and to guarantee that the coherence protocol is working properly along all the communicating nodes. In directory based cache coherence, this is done by using this directory to keep track of the status of all cache blocks, the status of each block includes in which cache coherence "state" that block is, and which nodes are sharing that block at that time, which can be used to eliminate the need to broadcast all the signals to all nodes, and only send it to the nodes that are interested in this single block.
