L1L2L3cache

L1, L2, and L3 caches are levels of hardware memory that bridge the speed gap between the CPU and main memory. They form a hierarchy that keeps copies of frequently used data and instructions close to the processor to reduce latency and memory traffic. L1 is the fastest and smallest, followed by L2 and L3 with increasing size and latency.

L1 caches are typically split into separate instruction and data caches on one or more cores. They are on-chip, very small (tens of kilobytes per core), and accessed in single-digit cycles. L1 caches often use write-back or write-through policies.

L2 caches are larger and slower than L1 and can be per-core or shared. They commonly range from hundreds of kilobytes to a few megabytes per core and are often unified (data and instructions).

L3 caches are the largest level and are frequently shared among cores. They reduce inter-core memory traffic and may be inclusive or exclusive with respect to L1/L2. L3 sizes are typically several megabytes to tens of megabytes, with higher latency than L2.

Coherence protocols such as MESI maintain consistency of cached data across cores. Cache misses are classified as compulsory, capacity, or conflict, and cache design choices influence performance and memory bandwidth.

Overall, L1/L2/L3 caches reflect a trade-off among speed, size, inclusivity, and coherence, shaping processor performance for a wide range of workloads.