L3 cache (Level 3 cache) is the largest and slowest of the processor's on-chip memory layers, sitting between the smaller, faster L1 and L2 caches and the main system RAM. When your CPU needs data, it checks L3 first before looking in slower main memory, which can take dozens of times longer to access.
Each core or group of cores in a processor has its own L1 and L2 cache, but L3 is typically shared across all cores. This shared pool helps multiple cores work together efficiently without duplicating data. Common L3 sizes range from 4 MB to 36 MB on consumer processors, and larger amounts generally offer better performance for demanding workloads.
Real-world example: When you're editing a large video file in Adobe Premiere, the processor repeatedly accesses specific chunks of the footage. If that data fits in L3 cache, the CPU retrieves it almost instantly. If the data keeps spilling out to main RAM, your editing software stutters and lags.
When evaluating a processor for your needs, check the L3 cache size alongside core count and clock speed. A processor with generous L3 cache handles multitasking and large files more smoothly, whilst a smaller cache may bottleneck performance in content creation or data-heavy applications. For everyday browsing and productivity, differences are negligible, but for gaming, video editing, or programming, L3 capacity matters.