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 hypnotic as we wait to see what kind of magic they’ll bring with their new generations of CPUs. More cores, less power draw, and much more performance.

But, when AMD’s CEO Lisa Su or Intel’s CEO Pat Gelsinger start explaining and breaking down the new technologies or chip architectures, you can’t but feel stumped and confused. One of the terms that are commonly thrown around to impress gamers is cache, specifically L1, L2, or L3 cache.

They are throwing this word around because it is actually very important for today’s processors, so let’s explain why that is.

Related:What Is A CPU?What CPU Do I Have?CPU Hierarchy 2021 – PC Processors Tier List

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What Is Cache?

What CPU Do I Have

The term cache is commonly used in the computing world. It is not unique to processors and is necessary for your PC to work as efficiently as it does.

For example, your browser constantly caches data of certain website images, templates, videos, etc. So, the next time you open that same website, your computer won’t have to waste any extra time, internet, and energy to process that data again. Instead, the browser will access its cache and open the site much faster.

The same applies to operating systems. The data stored in RAM is cached and it allows the operating system to be considerably more responsive.

Cache In CPUs

What Is A CPU

Is cache any different in CPUs? Its purpose is very similar, but it is different in some ways.

Processors are incredibly fast, but they need quick access to certain data to utilize that speed. Since regular system memory (DRAM) is simply too slow and too far away from the processor, the CPU has its own hardware cache that is considerably smaller and naturally, much closer to the CPU die. By reducing the communication distance, the whole process of accessing information is much faster.

So, yes, very similar to software (browser’s saved data) and hardware (RAM) cache, but there is still more to it.

L1, L2, Or L3 – What Is It?

CPU Hierarchy

You’ll notice CPU cache is always backed by the term L1, L2, L3, and sometimes even L4. These terms denote the multi-level cache used for CPUs.

So, L1 would be level 1, L2 is level 2, and L3, of course, level 3.

  • L1 is the fastest memory found in any consumer PC. It is considerably faster compared to other levels of cache or RAM. But, it is also much smaller in capacity because it is extremely expensive to make. These days L1 cache ranges between 256KB to no more than 1MB, but even that is enough since this memory is built directly into the CPUs cores. It is also important to note that every core gets 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, it is not as fast as L1, it’s located further away from the cores and it is shared among the cores in the CPU.
  • L3 is considerably larger than L1 and even L2 too. Intel’s i9-11900K has 16MB of L3 cache while AMD’s Ryzen 5950X has 64MB. Unlike L1, L2 and L3 cache 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?

In 2021 Computex, AMD announced they’ve managed to cram even more cache. This is all possible thanks to AMD’s new stacked Zen 3 chiplets.

Zen 3 processors will be getting 64MB of 7nm process cached, named 3D V-Cache. This will increase the L3 cache of these processors up to 192 MB which is triple the amount compared to regular Zen 3 chips. That’s considerably more.

However, Lisa Su also mentioned that 3D V-Cache is going to be huge for gamers. How? Well, based on AMD’s chart, a more and faster cache can impact gaming performance considerably.

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.

So, the only difference between these two CPUs is the speed and size of the cache. And even with such a small difference, the 3D stacked process provides up to 25% more FPS in Monster Hunter World over the 5900X. On average, it’s 15% faster in gaming.

That is the type of performance jump we usually see by jumping to a smaller process and not just by adding more cache.

But, maybe that’s the case only for AMD’s newer and faster cache. What about the memory found in CPUs from previous generations?

Looking at TechSpot’s extensive benchmarking and research, it seems like CPU cache definitely has a large impact on gaming.

They managed to test this by locking the i9-10900K (20MB cache) and i7-10700K (16 MB cache) to 8 cores and matching the frequency as well. That makes cache the only difference between these two SKUs.

In games such as Tom Clancy’s Rainbox Six Siege which isn’t very GPU bound, the 10900K beat the 10700K by about 5%. Benchmarks in Shadow of the Tomb Raider also showed similar differences in performance.

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

To further explore this idea, TechSpot dropped down to an even lower cache size. Locking both the i9-10900K and the i7-10700K to 6 cores and matching them to the same frequency as a 10600K which has only 12MB of cache.

In all games, the 10900K and 10700K were considerably faster. In some games, the 10900K is up to 20% faster than the 10600K. Those are huge numbers.

So, the final answer is yes! CPU cache does have a considerable impact on gaming performance. That impact probably translates to other tasks such as rendering or encoding too.

Conclusion

Intel CPU

A processor is an extremely complicated piece of hardware and everything on it has its own purpose and is extremely important. Removing even just one part will considerably hinder the CPU’s performance. Because of this, we can’t really determine the importance of CPU cache and how exactly it impacts gaming or productivity performance.

But, we did get a short insight with the benchmarks above. Showing us that CPU cache is vital and that improvements in speed or capacity in the future will surely bring more FPS in games, faster rendering, and more.

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Branko Gapo
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.