SOLVED: What is L1 L2 & L3 CPU Cache?

If you’ve ever looked at Task Manager on a Windows computer you will notice on the PERFORMANCE tab under CPU in the bottom right hand corner something labeled L1 cache, L2 cache and, L3 cache:

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To answer the question what is the difference between L1, L2, and L3 cache we will start with a brief explanation of what cache is.

What is CPU Cache?

Cache is simply high speed memory (chips) used to store data that the CPU just worked on and will need again, or data the CPU is guessing it will need soon and has buffered up.

CPU L1 L2 and L3 Cache Explained:

What is L1 Cache:

This is the smallest and fastest cache, located directly on the CPU core. It stores frequently accessed data and instructions to speed up processing. Think of it as your CPU’s personal assistant, always ready with the most critical information.

• Type: Typically SRAM (Static RAM)
• Speed: Fastest
• Size: Smallest (e.g., 32 KB per core)
• Location: Directly on the CPU core

What is L2 Cache:

Larger than L1 but slower, L2 cache is also located on the CPU but can be shared between cores. It acts as a middleman, holding data that isn’t as critical but still needs to be accessed quickly.

• Type: Also SRAM
• Speed: Slower than L1 but faster than L3
• Size: Larger than L1 (e.g., 1 MB per core)
• Location: On the CPU package, but can be shared between cores

What is L3 Cache:

This is the largest and slowest cache, shared across all CPU cores. It stores data that is less frequently accessed but still important for overall performance.

• Type: Typically SRAM
• Speed: Slowest among the three
• Size: Largest (e.g., up to 144 MB for high-end AMD Ryzen models)
• Location: On the CPU Package; Shared across all CPU cores

CPU Cache Size Examples

AMD Ryzen CPUs

• L1 Cache: 32 KB per core (L1I and L1D)
• L2 Cache: 1 MB per core
• L3 Cache: Varies by model, but can be up to 144 MB in total for high-end models like the Ryzen 9 7950X3D2.

Intel Core Ultimate CPUs

• L1 Cache: Typically 32 KB per core (L1I and L1D)
• L2 Cache: 1.25 MB per core
• L3 Cache: Varies by model, but can be up to 30 MB for high-end models like the Core Ultra 9 285HX

Why Not Just Have a Single Large CPU Cache?

There are two main reasons why there are different CPU caches:

1. PERFORMANCE: A single large cache would introduce higher latency, reducing the speed advantage. Different caches allow for a hierarchy where the most critical data is accessed the fastest, optimizing overall performance.
2. CACHE COSTS CASH: There is a substantial difference in the complexity of manufacturing, and hence the cost, of locating the SRAM cache closer to the CPU cores. L1 cache requires more precise and expensive manufacturing techniques to achieve its high speed and low latency, while L3 cache can be produced more economically due to its larger size and lower speed requirements..

While all three caches use SRAM, their speed and cost vary significantly due to their design and placement on the CPU. This hierarchical structure helps balance performance and cost effectively.

CPU Cache Sub-Types

You may see notations on L1I (“i” as in ‘instructions’) and L1D cache which gets confusing. Without getting weedy here are the definitions:

L1 Instruction Cache (L1I)

• Purpose: Stores instructions that the CPU needs to execute.
• Speed: Extremely fast, ensuring that the CPU can quickly fetch the instructions it needs.

L1 Data Cache (L1D)

• Purpose: Stores data that the CPU needs to process.
• Speed: Equally fast, allowing the CPU to access data without delay.

L2 & L3 Cache Sub-Types

L2 and L3 cache is “unified”, storing both instructions and data so there are typically no cache subtypes of L2 and L3 CPU cache.

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