What Is CPU Cache? (L1, L2, and L3 Cache)

What is CPU cache and what does L1 cache, L2 cache and L3 cache mean? How important is CPU cache when choosing a new CPU? Here's the ultimate guide.

Watching Intel or AMD keynotes at CES, Computex, or other events is always enthralling as we wait to see what sorts of magic they will introduce with their new generations of CPUs—these encompass more cores, diminished power draw, and significantly enhanced performance.

When AMD’s CEO Lisa Su or Intel’s CEO Pat Gelsinger starts explaining and breaking down the new technologies or chip architectures, however, it’s easy to get confused. One of the terms commonly thrown around to impress gamers is cache, specifically L1, L2, or L3 cache.

This word comes up so frequently because it is exceedingly significant for contemporary processors, so let’s delve into why this is the case.

Related:What Is A CPU?What CPU Do I Have?CPU Hierarchy 2023 – PC Processors Tier List

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What Is Cache?

What CPU Do I Have

The expression cache is often used in the computing world. It is not exclusive to processors, and it is essential for your PC to operate as effectively as it does.

For instance, your browser always stores data of website pictures, patterns, videos, etc. This suggests when you revisit that website, your computer won’t need to expend additional time, data, and power to handle that data again. Rather, the browser will just use its storage, and the site will load more rapidly.

This also applies to operating systems. The data stored in RAM is cached, enabling the operating system to be considerably more responsive.

Cache In CPUs

What Is A CPU

Is cache different in CPUs? Its function is very similar, but it varies in certain significant manners.

Processors operate very swiftly but need prompt access to specific data to fully utilize their speed. Since usual system memory (DRAM) is quite slow and distant from the processor, the CPU possesses its own hardware cache, which is relatively smaller and more proximate to the CPU chip. By minimizing the communication distance, the overall process of accessing information becomes significantly quicker.

This shows it’s similar to software (stored information in the browser) and hardware (RAM) caches, but there’s more to it still.

L1, L2, or L3—What Is It?

CPU Hierarchy

You may observe that CPU cache is always supported by the label L1, L2, L3, and occasionally even L4. These labels indicate the multilevel cache utilized for CPUs.

So, L1 would be tier one, L2 is tier two, and L3, of course, is tier three.

  • L1 is the fastest memory found in any consumer PC. It is considerably faster than other levels of cache or RAM. However, it is also much smaller in capacity because it is costly to make. These days, the L1 cache ranges from 256KB to no more than 1MB, but even that is sufficient since this memory is built directly into the CPU cores. It is also important to note every core receives a dedicated L1 cache.
  • L2 can have several times larger capacity than L1 (Ryzen 5900X has 6MB of L2 cache). L2 cache is usually a few megabytes and can go up to 10MB. However, L2 is not as fast as L1, it is located farther away from the cores, and it is shared among the cores in the CPU.
  • L3 is considerably larger than L1 and even L2. Intel’s i9-11900K has 16MB of L3 cache, while AMD’s Ryzen 5950X has 64MB. Unlike L1, L2 and L3 caches are shared between all cores. It is also the slowest memory on the CPU.
  • L4 is not very common; you won’t find it on any modern consumer CPU. It takes the form of DRAM compared to L1, L2, or L3 SRAM, and it is also placed separately from the chip.

To further optimize access to data, L1 is often split into L1d (for data) and L1i (for instructions).

cache latency
Cache latency from top (faster) to bottom (slower).

Does CPU Cache Impact Gaming Performance?

During the 2021 Computex, AMD announced they have managed to cram in even more cache. This is possible thanks to AMD’s new stacked Zen 3 chiplets.

Zen 3 processors will receive 64MB of 7nm process stored, named 3D V-Cache. This will increase the L3 cache of these processors up to 192 MB, which is three times the amount compared to regular Zen 3 chips; that is considerably more.

However, Lisa Su also mentioned that 3D V-Cache will be massive for gamers. Why? Well, based on AMD’s chart, a larger and faster cache can significantly impact gaming performance.

3D V Cache Technology Performance Uplift Across Gaming
5900X vs 3d-stacked 5900X frequency-matched at 4.0 GHz.

The image above shows a comparison between Zen 3 Ryzen 9 5900X fixed at 4.0 GHz against another 12-core processor (probably 5900X) that has been 3D stacked, also fixed at 4.0 GHz.

This means the only differences between the two CPUs are the speed and size of the cache. Even with such small differences, the 3D stacked process provides up to 25% more FPS in Monster Hunter World over the 5900X. On average, it is 15% faster in gaming.

This is the performance boost we typically see when jumping to a smaller process and not just by adding more cache.

However, this is maybe only the scenario for AMD’s more recent and faster cache. What about the memory found in CPUs from previous epochs?

Based on TechSpot’s thorough analysis and testing, it appears that CPU cache has a notable effect on gaming performance.

They were able to test this by locking the i9-10900K (20MB cache) and i7-10700K (16 MB cache) to eight cores and also matching the frequency. This makes the cache the only difference between these two SKUs.

In games like Tom Clancy’s Rainbow Six Siege, which isn’t heavily GPU dependent, the 10900K surpassed the 10700K by about 5%. Evaluations in Shadow of the Tomb Raider also showed comparable disparities in capability.

i9 10900K i7 10700K i5 10600K comparison
Comparison of i9-10900K, i7-10700K, and i5-10600K with core and frequency-matched.

To further delve into this concept, TechSpot descended to an even smaller cache size. They restricted both the i9-10900K and the i7-10700K to six cores and paired them with the identical clock speed as a 10600K, which possesses merely 12MB of cache.

In all games, the 10900K and 10700K were considerably faster. In some games, the 10900K was up to 20% faster than the 10600K—that is a huge difference.

So, the final answer is affirmative! CPU cache does have a noteworthy impact on gaming performance. That impact likely also translates to other tasks, such as rendering or encoding.

Conclusion

Intel CPU

A processor is a highly intricate piece of hardware, and each of its components has its own purpose and is immensely important. Removing just one part will greatly hinder the CPU’s performance. Because of this, we can’t truly determine the significance of CPU cache and how precisely it impacts gaming or productivity performance.

Still, we did gain a good understanding from the benchmarks mentioned. They indicate that CPU cache is essential, and enhancements in velocity or size in the upcoming times will undoubtedly result in higher FPS in games, swifter rendering, and additional benefits.

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Branko Gapo

Keeping up with the incredibly fast evolution of computer technology is almost impossible. That's why Branko will be using his knowledge on this matter to share news and information on all the latest essential technological innovations and advancements related to CPUs.