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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.
A write buffer is a type of data buffer that can be used to hold data being written from the cache to main memory or to the next cache in the memory hierarchy to improve performance and reduce latency. It is used in certain CPU cache architectures like Intel's x86 and AMD64. [1] In multi-core systems, write buffers destroy sequential consistency.
A write-through cache without write allocation A write-back cache with write allocation. Cache writes must eventually be propagated to the backing store. The timing for this is governed by the write policy. The two primary write policies are: [3] Write-through: Writes are performed synchronously to both the cache and the backing store.
The first stimulus is the processor-specific Read and Write request. For example: A processor P1 has a Block X in its Cache, and there is a request from the processor to read or write from that block. The second stimulus is given through the bus connecting the processors.
Data is written only in cache. Data is Write-Back to MM only when the data is replaced in cache or when required by other caches (see Write policy). It is better for multi-write on the same cache line. Intermediate solution: Write Through for the first write, Write-Back for the next (Write-once and Bull HN ISI [20] protocols). Write Allocate
In write-back mode, writes are written to the CPU's cache and the cache is marked dirty, so that its contents are written to memory later. Write-combining allows bus write transfers to be combined into a larger transfer before bursting them over the bus to allow more efficient writes to system resources like graphics card memory. This often ...
Processor requests to the cache include: PrRd: Processor request to read a cache block. PrWr: Processor request to write a cache block. State diagram of bus transactions for the MSI protocol. In addition, there are bus side requests. These include: BusRd: When a read miss occurs in a processor's cache, it sends a BusRd request on the bus and ...
However, with a multiple-level cache, if the computer misses the cache closest to the processor (level-one cache or L1) it will then search through the next-closest level(s) of cache and go to main memory only if these methods fail. The general trend is to keep the L1 cache small and at a distance of 1–2 CPU clock cycles from the processor ...