CPU Cache
The CPU cache is an integral part of the central processing unit architecture in modern computing systems. It is a high-speed memory component that stores frequently accessed data and instructions, enabling faster data retrieval for the processor. This system reduces the average time or energy required to access data from the main RAM.
Cache Hierarchy
The CPU cache operates on a hierarchical model that includes multiple levels such as L1 cache, L2 cache, and L3 cache. Occasionally, there might even be an L4 cache.
L1 Cache
The L1 cache, or Level 1 cache, is the smallest and fastest cache level. It is typically split into two separate caches: one for data (D-cache) and another for instructions (I-cache). The L1 cache is located within the processor cores, providing extremely fast access to its contents. Each core in a multicore processor usually has its own L1 cache, which is crucial for efficiency in instruction execution.
L2 Cache
The L2 cache is larger and slightly slower than the L1 cache. It serves as an intermediary between the fast L1 cache and the larger, slower main memory. The L2 cache can be shared among cores or dedicated to each core, depending on the CPU architecture. Its function is to store a larger set of data that may be accessed soon, reducing the need to fetch data from the main memory.
L3 Cache
The L3 cache, or Level 3 cache, is shared among all cores of the processor. It is larger and slower than both the L1 and L2 caches. The L3 cache acts as a reservoir for the L1 and L2 caches, storing a comprehensive collection of data and instructions that might be needed by any core. This setup improves the multi-threading capabilities of the processor.
Cache Coherency
In multicore processors, maintaining cache coherency is vital. This is achieved through protocols that ensure all caches in the system reflect the most recent version of any data stored. This coherence is particularly important in systems where multiple cores might attempt to access and modify the same data simultaneously.
Cache Replacement Policies
To efficiently manage the finite size of caches, cache replacement policies determine which data should be replaced when new data needs to be loaded. Common strategies include Least Recently Used (LRU), First-In-First-Out (FIFO), and Random Replacement.
Translation Lookaside Buffer
The Translation Lookaside Buffer (TLB) works closely with the CPU cache as part of the memory management unit. It stores recent translations of virtual memory to physical memory addresses, reducing the time needed for memory access.