Level 3 or L3 cache is specialized memory that works in conjunction with the L1 and L2 cache to improve the performance of the computer. The L1, L2, and L3 caches are computer processing unit (CPU) caches, as opposed to other types of caches in the system, such as hard drive cache. The CPU cache meets the needs of the microprocessor by anticipating data requests so that processing instructions are provided without delay. CPU cache is faster than random access memory (RAM) and is designed to avoid performance bottlenecks.
A central processing unit. The L3 cache is a CPU cache.
When a request is made to the system, the CPU requires instructions to execute that request. The CPU runs many times faster than system RAM, so to reduce delays, the L1 cache holds ready the bits of data it predicts will be needed. The L1 cache is very small, which allows it to be very fast. If the instructions are not present in the L1 cache, the CPU checks the L2, a slightly larger cache pool, with a slightly longer latency. With each cache miss, it moves to the next cache level. The L3 cache can be much larger than L1 and L2, and although it is also slower, it is still much faster than RAM retrieval.
The L3 cache used to be integrated into the motherboard in the past, but modern CPU models are now integrated with a native cache to increase performance.
Assuming the necessary instructions are in the L3 cache (a cache hit), bits of data can be evicted from the L1 cache to hold the new instructions, should they be needed again. The L3 cache may remove that instruction line, as it now resides in another cache (known as the exclusive cache), or it may remain in a copy (called the inclusive cache), depending on the design of the CPU.
For example, in November 2008, AMD® released its quad-core Shanghai chip. Each core has its own L1 and L2 caches, but the cores share a common L3 cache. L3 saves copies of the requested elements in case a later request is made by a different kernel.
The multilevel cache architecture continues to evolve. The L1 cache used to be external to the CPU, built into the motherboard, but now the L1 and L2 caches are usually built into the CPU chip. The L3 cache is normally integrated in the motherboard, but some CPU models are already incorporating the L3 cache. The advantage of having a built-in cache is that it is faster, more efficient, and less expensive than putting a separate cache on the motherboard.
Fetching instructions from the cache is faster than calling system RAM, and good cache design greatly improves system performance. Cache design and strategy will be different on various motherboards and CPUs, but all things being equal, the more cache the better.
