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Cache Coherency Protocols (examples)
Examples of coherency protocols for cache memory are listed here. For simplicity, all "miss" Read and Write status transactions which obviously come from state "I" (or miss of Tag), in the diagrams are not shown. They are shown directly on the new state. Many of the following protocols have only historical value. At the moment the main protocols used are the R-MESI type / MESIF protocols and the HRT-ST-MESI (MOESI type) or a subset or an extension of these. Cache coherency problem In systems as Multiprocessor system, multi-core and NUMA system, where a dedicated cache for each ''processor'', ''core'' or ''node'' is used, a consistency problem may occur when a same data is stored in more than one cache. This problem arises when a data is modified in one cache. This problem can be solved in two ways: # Invalidate all the copies on other caches (broadcast-invalidate) # Update all the copies on other caches (write-broadcasting), while the memory may be updated (write through) or ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Multiprocessor System Architecture
A multiprocessor system is defined as "a system with more than one processor", and, more precisely, "a number of central processing units linked together to enable parallel processing to take place". The key objective of a multiprocessor is to boost a system's execution speed. The other objectives are fault tolerance and application matching. The term "multiprocessor" can be confused with the term "multiprocessing". While multiprocessing is a type of processing in which two or more processors work together to execute multiple programs simultaneously, multiprocessor refers to a hardware architecture that allows multiprocessing. Multiprocessor systems are classified according to how processor memory access is handled and whether system processors are of a single type or various ones. Multiprocessor system types There are many types of multiprocessor systems: * Loosely coupled multiprocessor system * Tightly coupled multiprocessor system * Homogeneous multiprocessor system * H ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Illinois 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 a lot of bandwidth that is 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 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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bull HN ISI Protocol
A bull is an intact (i.e., not castrated) adult male of the species ''Bos taurus'' (cattle). More muscular and aggressive than the females of the same species (i.e., cows), bulls have long been an important symbol in many religions, including for sacrifices. These animals play a significant role in beef ranching, dairy farming, and a variety of sporting and cultural activities, including bullfighting and bull riding. Due to their temperament, handling requires precautions. Nomenclature The female counterpart to a bull is a cow, while a male of the species that has been castrated is a ''steer'', '' ox'', or ''bullock'', although in North America, this last term refers to a young bull. Use of these terms varies considerably with area and dialect. Colloquially, people unfamiliar with cattle may refer to both castrated and intact animals as "bulls". A wild, young, unmarked bull is known as a ''micky'' in Australia.Sheena Coupe (ed.), ''Frontier Country, Vol. 1'' (Weldon ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Write-once (or Write-first) Protocol
Write once may refer to: * Write once, run anywhere, a slogan for the cross-platform benefits of Java * Write once, compile anywhere, a slogan for the cross-platform benefits of C * Write-once (cache coherency) 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 ..., a write-invalidate protocol in computer memory design * Write once read many, computer storage that can be written to once, but read from multiple times {{disambig ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
AMD64
x86-64 (also known as x64, x86_64, AMD64, and Intel 64) is a 64-bit version of the x86 instruction set, first released in 1999. It introduced two new modes of operation, 64-bit mode and compatibility mode, along with a new 4-level paging mode. With 64-bit mode and the new paging mode, it supports vastly larger amounts of virtual memory and physical memory than was possible on its 32-bit predecessors, allowing programs to store larger amounts of data in memory. x86-64 also expands general-purpose registers to 64-bit, and expands the number of them from 8 (some of which had limited or fixed functionality, e.g. for stack management) to 16 (fully general), and provides numerous other enhancements. Floating-point arithmetic is supported via mandatory SSE2-like instructions, and x87/ MMX style registers are generally not used (but still available even in 64-bit mode); instead, a set of 16 vector registers, 128 bits each, is used. (Each register can store one or two double-precisi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
MOESI Protocol
(For a detailed description see Cache coherency protocols (examples)) 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. 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. ;Owned:This cache is one of several with ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Berkeley Protocol
Berkeley most often refers to: *Berkeley, California, a city in the United States **University of California, Berkeley, a public university in Berkeley, California *George Berkeley (1685–1753), Anglo-Irish philosopher Berkeley may also refer to: Places Australia * Berkeley, New South Wales, a suburb of Wollongong Canada * Berkeley, Ontario, a community in Grey County United Kingdom * Berkeley (hundred), an administrative division from late Saxon period to the 19th century * Berkeley, Gloucestershire, a town in England United States * Berkeley, California, a city in the San Francisco Bay Area, the largest city named Berkeley * Berkeley, Denver, a neighborhood in Denver, Colorado * Berkeley, Illinois, a suburb of Chicago * Berkeley, Missouri, a northwestern suburb of St. Louis * Berkeley Township, Ocean County, New Jersey * Berkeley, Rhode Island * Berkeley, Virginia (other) * Berkeley, West Virginia * Berkeley County (other) People * Berkeley (given n ... [...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 a lot of bandwidth that is 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 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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Firefly (DEC) Protocol
The Lampyridae are a family of elateroid beetles with more than 2,000 described species, many of which are light-emitting. They are soft-bodied beetles commonly called fireflies, lightning bugs, or glowworms for their conspicuous production of light, mainly during twilight, to attract mates. Light production in the Lampyridae is thought to have originated as an honest warning signal that the larvae were distasteful; this was co-opted in evolution as a mating signal in the adults. In a further development, female fireflies of the genus ''Photuris'' mimic the flash pattern of '' Photinus'' species to trap their males as prey. Fireflies are found in temperate and tropical climates. Many live in marshes or in wet, wooded areas where their larvae have abundant sources of food. While all known fireflies glow as larvae, only some species produce light in their adult stage, and the location of the light organ varies among species and between sexes of the same species. Fireflies h ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
PowerPC 7xx
The PowerPC 7xx is a family of third generation 32-bit PowerPC microprocessors designed and manufactured by IBM and Motorola (spun off as Freescale Semiconductor bought by NXP Semiconductors). This family is called the PowerPC G3 by its well-known customer Apple Inc., which introduced it on November 10, 1997. The term "PowerPC G3" is often, and incorrectly, imagined to be a microprocessor when in fact a number of microprocessors from different vendors have been used. Such designations were applied to Macintosh computers such as the PowerBook G3, the multicolored iMacs, iBooks and several desktops, including both the Beige and Blue and White Power Macintosh G3s. The low power requirements and small size made the processors ideal for laptops and the name lived out its last days at Apple in the iBook. The 7xx family is also widely used in embedded devices like printers, routers, storage devices, spacecraft, and video game consoles. The 7xx family had its shortcomings, namely lack ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Synapse Protocol
In the nervous system, a synapse is a structure that permits a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or to the target effector cell. Synapses are essential to the transmission of nervous impulses from one neuron to another. Neurons are specialized to pass signals to individual target cells, and synapses are the means by which they do so. At a synapse, the plasma membrane of the signal-passing neuron (the ''presynaptic'' neuron) comes into close apposition with the membrane of the target (''postsynaptic'') cell. Both the presynaptic and postsynaptic sites contain extensive arrays of molecular machinery that link the two membranes together and carry out the signaling process. In many synapses, the presynaptic part is located on an axon and the postsynaptic part is located on a dendrite or soma. Astrocytes also exchange information with the synaptic neurons, responding to synaptic activity and, in turn, regulating neurotransmission. Syn ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
