Cache memory is an indispensable component of every computer whose purpose is to store and give access to any necessary data. This temporary memory allows the processor to retrieve data efficiently and swiftly, and each feature of the cache memory contributes to this cause.

If you don’t know what these features are and are curious about the difference between L1, L2, and L3 cache in the processor, continue reading this detailed guide.

Difference Between L1, L2, and L3 Cache Memory

Cache memory stores data frequently used by the CPU, simply known as the processor. 

When information needs to be accessed, the CPU quickly searches through Level 1 cache memory, which is also referred to as internal or primary memory. This is the place where the data used most frequently is stored, as L1 is the fastest level of cache. 

Level 2 cache, on the other hand, is known as secondary or external memory. This is the second place that the CPU checks for necessary data, and as is the case with the primary cache, each core in the processor has its own L2 cache.

In case the data are not found, the Level 3 cache, that is, the external memory, will be searched as well in order to find the necessary information. Unlike primary and secondary cache, all the cores of the CPU share the same L3 cache memory.

Finally, if information can’t be found in any of the three segments, the RAM memory will be checked for data. Since the RAM memory is slower than the cache memory, the data found in one of the segments of the cache memory will result in a cache hit. On the other hand, the data found in the RAM memory is known as a cache miss. 

Let’s go over the most prominent differences among the three cache memory levels.

Further reading:

  • How to clear cache on iPhone?
  • How to clear browser cache?

Difference Between L1, L2, and L3 Cache: Locality

The primary, secondary, and external cache memories can be found in different locations, either on the processor itself or on a separate chip:

  • L1 cache, or internal cache, is built into the CPU chip itself;
  • L2 cache, also known as secondary or external cache, is tightly connected to the processor via a separate chip, referred to as a co-processor, while it can also be placed in the processor itself in some newer models of computers.
  • L3 cache, also known as Level 3 or external cache, is typically directly built into the motherboard. Nevertheless, some modern CPUs integrate L3 cache memory into the processor itself.

Difference Between L1, L2, and L3 Cache: Size

Cache memory size typically dictates the speed of retrieving information as well. The rule of thumb is that the smaller the memory, the faster it is. Here is the range of sizes for all three cache memory levels:

  • Level 1 cache memory is the smallest, and its size ranges between 8KB and 64KB;
  • Level 2 cache is bigger than L1 but smaller than L3, and its size ranges between 256 KB and 8 MB;
  • Level 3 cache is the largest one, and it thus takes the longest to access; Its size typically ranges between 10 MB to 64 MB;

Difference Between L1, L2, and L3 Cache: Association With CPU Cores

Nowadays, most CPUs have between 2 and 18 cores, and each cache level has a different association with those cores:

  • Since the L1 cache is internal and integrated into the processor, each CPU core has its own Level 1 cache memory;
  • L2 cache is an external cache located outside of the CPU. In newer models of processors, every CPU core has its own L2 cache, as opposed to older models in which the L2 cache is unified and shared by CPU cores.
  • L3 cache, unlike Level 1 and Level 2 caches, is generally unified and shared by all CPU cores.

Difference Between L1, L2, and L3 Cache: Speed

As previously mentioned, the three levels of cache memory differ in speed to a great extent. But, how fast are they actually? In general, it takes cache memory a few nanoseconds to complete the instruction. Let’s compare it to RAM memory’s speed for reference:

  • Level 1 cache reaches its maximum speed as soon as it’s accessed. In comparison, the L1 cache is 100 times faster than RAM memory.
  • Level 2 cache is faster than L3 but slower than L1 cache. This type of cache is 25 times faster than RAM memory.
  • Level 3 cache is the slowest, as well as the biggest cache. Nevertheless, it’s still twice as fast as RAM memory.

Difference Between L1, L2, and L3 Cache: Specialisation and Functionality

All features of the primary, secondary, and external cache memories dictate their purpose and functionality. These are their basic goals while taking into account their size, speed, and placement:

  • L1 cache, being the fastest type of cache memory, is used to store information that is frequently used by the CPU;
  • L2 cache stores and provides data to the processor without any delays and hold-ups;
  • L3 cache is a specialised cache much larger than L1 and L2 combined, and it’s used to manage inter-core communication and improve the performance of Level 1 and Level 2 cache.

Summary Table

1. What does the CPU cache do?

The CPU cache holds onto information that the processor frequently uses, for a certain period of time, allowing for fast and easy access. 

2. Which cache levels are usually built onto the processor chip?

L1 cache is typically integrated into the processor chip. On the other hand, L2 cache can be found on a separate chip in older models and on the processor chip in newer models of computers. Finally, the L3 cache is built onto the motherboard and therefore separated from the CPU chip.

3. Does the L3 cache make a difference?

The L3 cache is twice as fast as RAM memory and much bigger than both the L1 and L2 cache, making this the biggest difference between L1, L2, and L3 cache in the processor. Therefore, its main function is to provide better performance for L1 and L2.