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MOSI Protocol
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. Overview of States Following are the permitted states of a given cache line: Modified (M) - Only one cache has a valid copy of the block and the value is likely to be different from the one in main memory. It has almost the same meaning as a dirty state in a write-back cache except for the difference that modified state also implies exclusive ownership of that block. Dirty state just means that the value of the block is different from the one in main memory, whereas, modified implies that the value is different than that of the main memory and that it is cached in only one location. Owned (O) - Multiple caches may hold the most recent and correct value of a block and the value in main memory may or may not be correct. At a time, only one cache can have the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
MSI Protocol
In computing, the MSI protocol - a basic Cache coherence, 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. Overview In MSI, each block contained inside a cache can have one of three possible states: *Modified: The block has been modified in the CPU cache, cache. The data in the cache is then inconsistent with the backing store (e.g. Main memory, memory). A cache with a block in the "M" state has the responsibility to write the block to the backing store when it is evicted. *Shared: This block is unmodified and exists in read-only state in at least one cache. The cache can evict the data without writing it to the backing store. *Invalid: This block is either not present in the current cache or has been invalidated by a bus request, and must be fetched from memory or another CPU cache, cache if the block is to be stored in this cac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cache Coherency
In computer architecture, cache coherence is the uniformity of shared resource data that is stored in multiple local caches. In a cache coherent system, if multiple clients have a cached copy of the same region of a shared memory resource, all copies are the same. Without cache coherence, a change made to the region by one client may not be seen by others, and errors can result when the data used by different clients is mismatched. A cache coherence protocol is used to maintain cache coherency. The two main types are snooping and directory-based protocols. Cache coherence is of particular relevance in multiprocessing systems, where each CPU may have its own local cache of a shared memory resource. Overview In a shared memory multiprocessor system with a separate cache memory for each processor, it is possible to have many copies of shared data: one copy in the main memory and one in the local cache of each processor that requested it. When one of the copies of data is c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Protocol (computing)
A communication protocol is a system of rules that allows two or more entities of a communications system to transmit information via any variation of a physical quantity. The protocol defines the rules, syntax, semantics, and synchronization of communication and possible error recovery methods. Protocols may be implemented by hardware, software, or a combination of both. Communicating systems use well-defined formats for exchanging various messages. Each message has an exact meaning intended to elicit a response from a range of possible responses predetermined for that particular situation. The specified behavior is typically independent of how it is to be implemented. Communication protocols have to be agreed upon by the parties involved. To reach an agreement, a protocol may be developed into a technical standard. A programming language describes the same for computations, so there is a close analogy between protocols and programming languages: ''protocols are to communica ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Write-back Cache
In computing, a cache ( ) is a hardware or software component that stores data so that future requests for that data can be served faster; the data stored in a cache might be the result of an earlier computation or a copy of data stored elsewhere. A cache hit occurs when the requested data can be found in a cache, while a cache miss occurs when it cannot. Cache hits are served by reading data from the cache, which is faster than recomputing a result or reading from a slower data store; thus, the more requests that can be served from the cache, the faster the system performs. To be cost-effective, caches must be relatively small. Nevertheless, caches are effective in many areas of computing because typical computer applications access data with a high degree of locality of reference. Such access patterns exhibit temporal locality, where data is requested that has been recently requested, and spatial locality, where data is requested that is stored near data that has already bee ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
MOSI Processor Transactions
Mosi or MOSI may refer to: * Mosi (given name) * Mosi (surname) * Molybdenum silicide (MoSi2), an important material in the semiconductor industry * MOSI protocol, an extension of the basic MSI cache coherency protocol * MOSI, Master Out Slave In (data output from master), Serial Peripheral Interface pin and logic signal * Museum of Science and Industry (MOSI), former name of the Science and Industry Museum The Science and Industry Museum in Manchester, England, traces the development of science, technology and industry with emphasis on the city's achievements in these fields. The museum is part of the Science Museum Group, a non-departmental pu ... in Manchester, England * Mosi (beer) See also * Museum of Science and Industry (other), several museums {{disambiguation ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bus Snooping
Bus snooping or bus sniffing is a scheme by which a coherency controller (snooper) in a cache (a snoopy cache) monitors or snoops the bus transactions, and its goal is to maintain a cache coherency in distributed shared memory systems. This scheme was introduced by Ravishankar and Goodman in 1983, under the name "write-once" cache coherency. A cache containing a coherency controller (snooper) is called a snoopy cache. How it works When specific data are shared by several caches and a processor modifies the value of the shared data, the change must be propagated to all the other caches which have a copy of the data. This change propagation prevents the system from violating cache coherency. The notification of data change can be done by bus snooping. All the snoopers monitor every transaction on a bus. If a transaction modifying a shared cache block appears on a bus, all the snoopers check whether their caches have the same copy of the shared block. If a cache has a copy of the s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
MOSI Bus Transactions Updated
Mosi or MOSI may refer to: * Mosi (given name) * Mosi (surname) * Molybdenum silicide (MoSi2), an important material in the semiconductor industry * MOSI protocol, an extension of the basic MSI cache coherency protocol * MOSI, Master Out Slave In (data output from master), Serial Peripheral Interface pin and logic signal * Museum of Science and Industry (MOSI), former name of the Science and Industry Museum The Science and Industry Museum in Manchester, England, traces the development of science, technology and industry with emphasis on the city's achievements in these fields. The museum is part of the Science Museum Group, a non-departmental pu ... in Manchester, England * Mosi (beer) See also * Museum of Science and Industry (other), several museums {{disambiguation ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
MESI Protocol
The MESI protocol is an invalidate-based cache coherence protocol, and is one of the most common protocols that support write-back caches. It is also known as the Illinois protocol due to its development at the University of Illinois at Urbana-Champaign. Write back caches can save considerable bandwidth generally wasted on a write through cache. There is always a dirty state present in write-back caches that indicates that the data in the cache is different from that in the main memory. The Illinois Protocol requires a cache-to-cache transfer on a miss if the block resides in another cache. This protocol reduces the number of main memory transactions with respect to the MSI protocol. This marks a significant improvement in performance. States The letters in the acronym MESI represent four exclusive states that a cache line can be marked with (encoded using two additional bits): ;Modified (M): The cache line is present only in the current cache, and is ''dirty'' - it has been m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coherence Protocol
In computer architecture, cache coherence is the uniformity of shared resource data that is stored in multiple local caches. In a cache coherent system, if multiple clients have a cached copy of the same region of a shared memory resource, all copies are the same. Without cache coherence, a change made to the region by one client may not be seen by others, and errors can result when the data used by different clients is mismatched. A cache coherence protocol is used to maintain cache coherency. The two main types are snooping and directory-based protocols. Cache coherence is of particular relevance in multiprocessing systems, where each CPU may have its own local cache of a shared memory resource. Overview In a shared memory multiprocessor system with a separate cache memory for each processor, it is possible to have many copies of shared data: one copy in the main memory and one in the local cache of each processor that requested it. When one of the copies of data is ch ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
MOESI Protocol
Modified Owned Exclusive Shared Invalid (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 . In order for this to be possible, direct cache-to-cache transfers of data must be possible, so a cache with the data in the modified state can supply that data to another reader without transferring it to memory. As discussed in AMD64 Architecture Programmer's Manual Vol. 2 ''System Programming'', each cache line is in one of five states: ;Modified: This cache has the only valid copy of the cache line, and has made changes to that copy. The cached copy may be further modified freely. ;Owned: This line is one of seve ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
