In a CPU, what exactly is a "cache"? I was wondering what exactly a "Cache" is in a CPU. Why does having a larger cache improve performance? In the Phenom II and Core i7 processors, I noticed that they have a small ammount of L2, and L3 cache, and 8 MB of L4 cache per core. What does this mean? The Core 2 processors only have 3 MB of L2 cache per core. How much of a performance increase do you get with the larger caches?