Computer processors use a hierarchy of caches to store information and reduce the amount of time required to access memory. A level 2 cache, also known as a secondary cache, comes into play when the computer needs to access recently accessed data for a second time. Caches provide quicker access to information than regular memory and can greatly improve the responsiveness of your computer. Several caches can store additional information, resulting in a snappier computing experience.
Cache Levels
The level 1 cache usually consists of two parts -- one stores data and the other stores instructions needed to execute programs and commands. The L1 cache provides the fastest rates and sits directly on the processor chip. Often, the L1 cache rate operates at the same, or nearly the same, speed as the processor. The level 2 cache sits on the processor module and sometimes directly on the chip. An L2 cache acts as the next level down, runs slightly slower than the L1 cache and typically only stores data.
Cache Size
A cache acts as a smaller, faster form of memory used to access recently used information. Large cache sizes increase the amount of information that the system can store. However, large caches take longer to retrieve information. Manufacturers accommodate this by using several caches of different sizes. The higher-level caches work faster but store less information. These smaller, higher-level caches are backed up by larger but slower caches. When looking for information, the computer first checks the L1 cache before checking the L2 or even an L3 cache.
Cache Latency
A 3MB L2 cache usually provides better latency than a 6MB L2 cache. Latency refers to the amount of time it takes to access information. While you may assume that a larger cache would provide better performance, because the computer needs to sift through additional information, the larger cache can slow down your computer. Because of this consideration, a multicache system with smaller caches on each level provides better performance than a two-cache system with larger caches. However, as caching technology continues to improve, manufacturers have started increasing the size of the L2 cache size because the system can usually find the information needed on the L1 cache.
Cache Hit Rate
Cache hit rate refers to the rate at which the processor finds the information it needs on a given cache. Even though a smaller cache provides reduced latency, the hit rate of a cache can suffer on systems with a smaller L2 cache. Because a 3MB cache stores half the information of a system with a 6MB cache, the computer may need to go to a lower-level cache to find the data it needs. Caches work faster than system memory, so the processor looks to the available caches first to find the needed data or instructions.
