L1, L2, and L3 caches are CPU caches that anticipate requests for data to prevent performance bottlenecks. L1 is very small and fast, while L3 is larger and slower but still faster than RAM. Multilevel caching architecture continues to evolve, with some CPU models incorporating L3 cache. Good cache design improves system performance significantly.
Level 3 or L3 cache is specialized memory that works hand in hand with L1 and L2 cache to improve computer performance. L1, L2, and L3 caches are computer processing unit (CPU) caches, as opposed to other types of caches in the system such as hard drive cache. The CPU cache satisfies the needs of the microprocessor by anticipating requests for data so that processing instructions are provided without delay. CPU cache is faster than random access memory (RAM) and is designed to prevent performance bottlenecks.
When a system request is made, the CPU requests instructions to carry out that request. The CPU runs many times faster than the system RAM, so to reduce delays, the L1 cache has data bits ready that it predicts will be needed. The L1 cache is very small which allows it to be very fast. If the instructions are not in L1 cache, the CPU checks L2, a slightly larger cache pool, with somewhat longer latency. With each cache miss you look at the next level of cache. L3 cache can be much larger than L1 and L2, and while it’s also slower, it’s still much faster than fetching from RAM.
Assuming the needed instructions are in the L3 cache (a cache hit), data bits could be dropped from the L1 cache to hold new instructions in case they are needed again. The L3 cache can then evict that line of instructions as it now resides in another cache (called an exclusive cache) or it could get stuck on a copy (called an inclusive cache), depending on the CPU design.
For example, in November 2008 AMD® released its quad-core Shanghai chip. Each core has its own L1 and L2 cache, but the cores share a common L3 cache. L3 keeps copies of requested items in case a different core makes a later request.
The architecture for multilevel caching continues to evolve. L1 cache used to be external to the CPU, built into the motherboard, but now both L1 and L2 caches are commonly built into the CPU die. L3 cache has typically been built into the motherboard, but some CPU models already incorporate L3 cache. The benefit of having an onboard cache is that it is faster, more efficient, and less expensive than putting a separate cache on the motherboard.
Retrieving instructions from the cache is faster than using system RAM, and good cache design improves system performance significantly. Cache design and strategy will be different on various motherboards and CPUs, but all else being equal, more cache is better.
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