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A CPU cache is a hardware cache used by the central processing unit (CPU) of a computer to reduce the average cost (time or energy) to access data from the main memory. [1] A cache is a smaller, faster memory, located closer to a processor core, which stores copies of the data from frequently used main memory locations.
Cache hierarchy, or multi-level cache, is a memory architecture that uses a hierarchy of memory stores based on varying access speeds to cache data. Highly requested data is cached in high-speed access memory stores, allowing swifter access by central processing unit (CPU) cores.
The number of levels in the memory hierarchy and the performance at each level has increased over time. The type of memory or storage components also change historically. [6] For example, the memory hierarchy of an Intel Haswell Mobile [7] processor circa 2013 is: Processor registers – the fastest possible access (usually 1 CPU cycle). A few ...
Imagine a CPU equipped with a cache and an external memory that can be accessed directly by devices using DMA. When the CPU accesses location X in the memory, the current value will be stored in the cache. Subsequent operations on X will update the cached copy of X, but not the external memory version of X, assuming a write-back cache. If the ...
The main uncore interface to the core is the so-called cache box (CBox), which interfaces with the last level cache (LLC) and is responsible for managing cache coherency. Multiple internal and external QPI links are managed by physical-layer units, referred to as PBox.
A victim cache is a small, typically fully associative cache placed in the refill path of a CPU cache. It stores all the blocks evicted from that level of cache and was originally proposed in 1990. In modern architectures, this function is typically performed by Level 3 or Level 4 caches.
Cache prefetching can be accomplished either by hardware or by software. [3]Hardware based prefetching is typically accomplished by having a dedicated hardware mechanism in the processor that watches the stream of instructions or data being requested by the executing program, recognizes the next few elements that the program might need based on this stream and prefetches into the processor's ...
A drawback of an inclusive policy is that the unique memory capacity of the cache is determined by the lower level cache. Unlike the case of exclusive cache, where the unique memory capacity is the combined capacity of all caches in the hierarchy. [4]