Cache - intermediate buffer with quick access A that contains the information that is most likely to be requested. Access to data in the cache is faster than fetching initial data from operational (RAM) and faster than external ( HDD or solid state drive) memory, which reduces the average access time and increases overall performance computer system.

A number of central processing unit (CPU) models have their own cache in order to minimize access to random access memory(RAM), which is slower than registers. Cache memory can provide significant performance gains when the RAM clock speed is significantly lower than the CPU clock speed. The clock speed for the cache memory is usually not much less than the CPU frequency.

Cache levels

Cache CPU divided into several levels. In a general purpose processor, the number of levels can currently be as high as 3. Level N+1 caches are typically larger and slower in access and data transfer rates than level N caches.

most fast memory is the first level cache -- L1-cache. In fact, it is an integral part of the processor, since it is located on the same chip with it and is part of the functional blocks. In modern processors, the L1 cache is usually divided into two caches, the instruction (instruction) cache and the data cache (Harvard architecture). Most processors without an L1 cache cannot function. L1 cache operates at the processor frequency, and, in general, it can be accessed every clock cycle. It is often possible to perform multiple read/write operations at the same time. Access latency is typically 2-4 core cycles. The volume is usually small - no more than 384 KB.

The second fastest is L2-cache - a second-level cache, usually it is located on a chip, like L1. In older processors, the chipset on system board. The volume of L2 cache is from 128 KB to 1x12 MB. In modern multi-core processors the second-level cache, located on the same chip, is a separate memory - with a total cache size of nM MB, each core has nM / nC MB, where nC is the number of processor cores. Typically, the latency of the L2 cache located on the core chip is from 8 to 20 core cycles.

The third level cache is the least fast, but it can be very impressive in size - more than 24 MB. The L3 cache is slower than previous caches, but still significantly faster than RAM. In multiprocessor systems, it is in common use and is designed to synchronize data of various L2.

Sometimes there is also a level 4 cache, usually it is located in a separate chip. The use of a level 4 cache is justified only for high-performance servers and mainframes.

Synchronization problem between various caches(both one and many processors) is solved by cache coherence. There are three options for exchanging information between caches of different levels, or, as they say, cache architectures: inclusive, exclusive, and non-exclusive.

While doing various tasks the processor of your computer receives the necessary blocks of information from the RAM. Having processed them, the CPU writes the results of calculations to memory and receives subsequent blocks of data for processing. This continues until the task is completed.

The above processes are carried out at a very high speed. However, the speed of even the fastest RAM is significantly less than the speed of any weak processor. Each action, whether it is writing information to it or reading from it, takes a lot of time. The speed of the RAM is ten times lower than the speed of the processor.

Despite such a difference in the speed of information processing, the PC processor is not idle and does not wait for the RAM to issue and receive data. The processor is always working and all thanks to the presence of cache memory in it.

Cache is a special kind of RAM. The processor uses cache memory to store those copies of information from the computer's main RAM that are likely to be accessed in the near future.

In essence, the cache memory acts as a high-speed memory buffer that stores information that the processor may need. Thus, the processor receives the necessary data ten times faster than when reading them from RAM.

The main difference between a cache memory and a regular buffer is the built-in logic functions. The buffer stores random data, which is usually processed according to the "first received, first issued" or "first received, last issued" scheme. The cache contains data that is likely to be accessed in the near future. Therefore, thanks to the “smart cache”, the processor can run at full speed and not wait for data to be retrieved from slower RAM.

Main types and levels of L1 L2 L3 cache

Cache memory is made in the form of static random access memory (SRAM) chips that are installed on the system board or built into the processor. Compared to other types of memory, static memory can operate at very high speeds.

The cache speed depends on the size of a particular chip. The larger the size of the chip, the more difficult it is to achieve high speed for its operation. Considering this feature, during manufacture, the cache memory of the processor is made in the form of several small blocks called levels. The most common today is the three-level cache system L1, L2, L3:

Cache memory of the first level L1 - the smallest in volume (only a few tens of kilobytes), but the fastest in speed and the most important. It contains the data most frequently used by the processor and runs without delay. Typically, the number of L1 memory chips is equal to the number of processor cores, with each core accessing only its own L1 chip.

L2 cache it is inferior to L1 memory in speed, but wins in volume, which is already measured in several hundred kilobytes. It is for temporary storage. important information, the probability of accessing which is lower than that of the information stored in the L1 cache.

Third level L3 cache - has the largest volume of the three levels (it can reach tens of megabytes), but also has the most slow speed, which is still significantly higher than the speed of RAM. The L3 cache is shared across all processor cores. The memory level L3 is intended for temporary storage of those important data, the probability of accessing which is slightly lower than that of the information stored in the first two levels L1, L2. It also ensures the interaction of the processor cores with each other.

Some processor models are made with two levels of cache memory, in which L2 combines all the functions of L2 and L3.

When a large amount of cache is useful.

You will feel a significant effect from a large amount of cache when using archiver programs, in 3D games, during video processing and encoding. In relatively "light" programs and applications, the difference is practically not noticeable (office programs, players, etc.).

Good day to all. Today we will try to explain to you such a thing as a cache. The processor cache is an ultra-fast data processing array that is 16-17 times faster than standard RAM when it comes to DDR4.

From this article you will learn:

It is the amount of cache memory that allows the CPU to operate at maximum speeds, without waiting for the RAM to process any data and send the results of the finished calculations to the chip for further processing. A similar principle can be traced in the HDD, only a buffer of 8–128 MB is used there. Another thing is that the speeds are much lower, but the process is similar.

What is a processor cache?

How does the calculation process work in general? All data is stored in RAM, which is designed for temporary storage of important user and system information. The processor chooses for itself a certain number of tasks, which are driven into an ultra-fast block called cache memory, and begins to do its direct duties.

The calculation results are again sent to RAM, but in a much smaller amount (instead of a thousand output values, we get much less), and a new array is taken for processing. And so on until the job is done.

The speed of work is determined by the efficiency of RAM. But not a single modern DDR4 module, including overclocking solutions with frequencies under 4000 MHz, came close to the capabilities of the most stunted processor with its “slow” cache.

This is because the speed of the CPU exceeds the performance of the RAM on average 15 times, or even higher. And do not look only at the frequency parameters, in addition to them there are enough differences.
In theory, it turns out that even heavy-duty Intel Xeon and AMD Epyc are forced to idle, but in fact both server chips are working at their limit. And all because they collect the required amount of data by the size of the cache (up to 60 MB or more) and process the data instantly. RAM serves as a kind of warehouse from which arrays are scooped for calculations. The computing efficiency of the computer increases and everyone is happy.

A brief excursion into history

The first mention of cache memory dates back to the end of the 80s. Until that time, the speed of the processor and memory were approximately the same. The rapid development of chips required some kind of “crutch” to increase the speed of RAM, but using ultra-fast chips was very expensive, and therefore they decided to get by with a more economical option - the introduction of a high-speed memory array in the CPU.

The first cache memory module appeared in the Intel 80386. At that time, DRAM latencies hovered around 120 nanoseconds, while a more modern SRAM module reduced latency to an impressive 10 nanoseconds at that time. An approximate picture is more clearly demonstrated in the confrontation between HDD and SSD.

Initially, the cache memory was soldered directly to motherboards, due to the level of the technical process of that time. Starting with the Intel 80486, 8 kb of memory was incorporated directly into the processor die, further increasing performance and reducing die area.

This layout technology remained relevant only until the release of Pentium MMX, after which SRAM-memory was replaced by more advanced SDRAM.
And the processors have become much smaller, and therefore the need for external circuits has disappeared.

Cache levels

On the marking of modern CPUs, in addition to and, you can find such a thing as a cache size of 1,2 and 3 levels. How is it defined and what does it affect? Let's understand in simple terms.

• The first level (L1) cache is the most important and fastest chip in the CPU architecture. One processor can accommodate the number of modules equal to the number of cores. It is noteworthy that the microcircuit can store in memory the most demanded and important data only from its core. The size of the array is often limited to 32-64 KB.
• Cache of the second level (L2) - the drop in speed is compensated by an increase in the size of the buffer, which reaches 256 or even 512 KB. The principle of operation is the same as that of L1, but the frequency of memory requests is lower, due to the storage of less priority data in it.
• The third level (L3) cache is the slowest and most voluminous partition among all those listed. Still, this array is much faster than RAM. The size can reach 20, and even 60 MB, when it comes to server chips. The benefit of the array is enormous: it is a key link in the exchange of data between all the cores of the system. Without L3, all elements of the chip would be scattered.

On sale you can find both two- and three-level memory structure. Which one is better? If you are using the processor only for office programs and casual games, you will not feel any difference. If the system is assembled with an eye on complex 3D games, archiving, rendering and graphics, then the increase in some cases will range from 5 to 10%.
A L3 cache is justified only if you intend to regularly work with multi-threaded applications that require regular complex calculations. For this reason, server models often use large L3 caches. Although there are times when this is not enough, and therefore you have to additionally install the so-called L4 modules, which look like a separate microcircuit connected to the motherboard.

How to find out the number of levels and cache size on your processor?

Let's start with the fact that this can be done in 3 ways:

• through command line(only L2 and L3 cache);
• by searching for specifications on the Internet;
• using third party utilities.

If we take as a basis the fact that for most processors L1 is 32 KB, and L2 and L3 can fluctuate widely, we need the last 2 values. To search for them, open the command line through the "Start" (enter the value "cmd" through the search bar).

The system will show a suspiciously high value for L2. You need to divide it by the number of processor cores and find out the final result.

If you are going to search for data on the network, then first find out the exact name of the CPU. Click right click on the "My Computer" icon and select "Properties". In the column "System" there will be an item "Processor", which we actually need. Rewrite its name in the same Google or Yandex and see the value on the sites. For reliable information, it is better to choose the official portals of the manufacturer (Intel or AMD).
The third method also does not cause problems, but requires the installation of additional software such as GPU-Z, AIDA64 and other utilities to study the specifications of the stone. An option for fans of overclocking and swarming in detail.

Results

Now you understand what cache memory is, what determines its volume, and for what purposes an ultra-fast data array is used. On the this moment The most interesting solutions on the market in terms of large cache memory are AMD Ryzen 5 and 7 devices with their 16 MB L3.

In the following articles, we will cover topics such as processors, the benefits of chips, and more. and stay with us. Until we meet again, bye.

Welcome to GECID.com! It is well known that the clock speed and the number of processor cores directly affect the level of performance, especially in projects optimized for multithreading. We decided to check what role the L3 cache memory plays in this?

To investigate this issue, we were kindly provided by the pcshop.ua online store with a 2-core processor with a nominal operating frequency of 3.7 GHz and 3 MB of L3 cache with 12 associativity channels. The 4-core one acted as an opponent, in which two cores were disabled and the clock frequency was reduced to 3.7 GHz. It has 8 MB L3 cache and 16 associativity channels. That is, the key difference between them lies precisely in the cache of the last level: the Core i7 has 5 MB more of it.

If this has a noticeable effect on performance, then it will be possible to conduct another test with a representative of the Core i5 series, which has 6 MB of L3 cache on board.

But for now, back to the current test. The participants will be assisted by a video card and 16 GB of DDR4-2400 MHz RAM. We will compare these systems in Full HD resolution.

To begin with, let's start with out-of-sync live gameplays in which it is impossible to unambiguously determine the winner. AT Dying Light at maximum quality settings, both systems show a comfortable FPS level, although the processor and video card load was higher on average in the case of Intel Core i7.

Arma 3 has a well-pronounced processor dependence, which means that a larger amount of cache memory should play a positive role even at ultra-high graphics settings. Moreover, the load on the video card in both cases reached a maximum of 60%.

A game DOOM on ultra-high graphics settings, it only allowed to synchronize the first few frames, where the advantage of the Core i7 is about 10 FPS. The desynchronization of further gameplay does not allow determining the degree of influence of the cache on the speed of the video sequence. In any case, the frequency was kept above 120 frames / s, so even 10 FPS does not have a special effect on the comfort of passing.

Completes a mini-series of live gameplay Evolve Stage 2. Here we would surely see the difference between the systems, since in both cases the video card is approximately half loaded. Therefore, subjectively, it seems that the FPS level in the case of Core i7 is higher, but it is impossible to say for sure, since the scenes are not identical.

Benchmarks provide a more informative picture. For example, in gta v you can see that outside the city the advantage of 8 MB cache reaches 5-6 frames / s, and in the city - up to 10 FPS due to the higher loading of the video card. At the same time, the video accelerator itself in both cases is far from being loaded to the maximum, and it all depends on the CPU.

The Third Witcher we launched with outrageous graphics settings and a high post-processing profile. In one of the scripted scenes, the advantage of the Core i7 in some places reaches 6-8 FPS with a sharp change in angle and the need to load new data. When the load on the processor and video card again reaches 100%, the difference decreases to 2-3 frames.

Max preset graphic settings in XCOM 2 did not become a serious test for both systems, and the frame rate was in the region of 100 FPS. But here, too, a larger amount of cache memory was transformed into an increase in speed from 2 to 12 frames / s. And although both processors failed to load the video card to the maximum, the 8 MB version did better in this matter in some places.

The most amazing game Dirt Rally, which we launched with a very high preset. At certain points, the difference reached 25 frames / s solely due to the larger L3 cache. This allowed for 10-15% better loading of the video card. However, the average benchmark results showed a more modest victory for the Core i7 - only 11 FPS.

An interesting situation arose with Rainbow Six Siege: on the street, in the first frames of the benchmark, the Core i7 advantage was 10-15 FPS. Indoors, the CPU and video card loading in both cases reached 100%, so the difference decreased to 3-6 FPS. But at the end, when the camera moved out of the house, the Core i3 lagged again in places over 10 fps. The average figure turned out to be at the level of 7 FPS in favor of 8 MB of cache.

The Division at maximum quality graphics also respond well to increased cache memory. Already the first frames of the benchmark fully loaded all the Core i3 threads, but the total load on the Core i7 was 70-80%. However, the difference in speed at these moments was only 2-3 FPS. A little later, the load on both processors reached 100%, and at certain points the difference was already beyond the Core i3, but only by 1-2 frames / s. On average, it was about 1 FPS in favor of the Core i7.

In turn, the benchmarkRise of Tomb Riderat high graphics settings in all three test scenes, it clearly showed the advantage of a processor with a significantly larger cache memory. Its average performance is 5-6 FPS better, but if you carefully look at each scene, then in some places the Core i3 lags more than 10 frames / s.

But when choosing a preset with very high settings, the load on the video card and processors increases, so for the most part the difference between systems decreases to a few frames. And only for a short time Core i7 can show more significant results. According to the results of the benchmark, the average indicators of its advantage decreased to 3-4 FPS.

Hitman also less affected by the L3 cache. Even here, though, at the ultra-high detail profile, the extra 5 MB provided better graphics card loading, turning that into an additional 3-4 fps. They do not have a particularly critical effect on performance, but out of purely sporting interest, it is nice that there is a winner.

High graphics settings Deus ex: Mankind divided immediately demanded maximum processing power from both systems, so the difference in best case was 1-2 frames in favor of the Core i7, as indicated by the average.

Re-running at the ultra-high preset loaded the graphics card even more, so the impact of the processor on the overall speed became even less. Accordingly, the difference in the L3 cache had practically no effect on the situation, and the average FPS differed by less than half a frame.

According to the results of testing, it can be noted that the effect of L3 cache memory on performance in games does take place, but it only manifests itself when the video card is not loaded at full capacity. In such cases, it would be possible to get an increase of 5-10 FPS if the cache was increased by 2.5 times. That is, approximately it turns out that, other things being equal, each additional MB of L3 cache adds only 1-2 FPS to the video sequence display speed.

So, if we compare neighboring lines, for example, Celeron and Pentium, or models with different L3 cache sizes inside the Core i3 series, then the main performance increase is achieved due to more high frequencies, and then the presence of additional processor threads and cores. Therefore, when choosing a processor, first of all, nevertheless, you need to focus on the main characteristics, and only then pay attention to the amount of cache memory.

That's all. Thank you for your attention. We hope this material was useful and interesting.

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Today's article is not an independent material - it simply continues the study of the performance of three generations of the Core architecture in equal conditions (begun at the end of last year and continued recently). True, today we will take a small step to the side - the frequencies of the cores and cache memory will remain the same as before, but the capacity of the latter will decrease. Why is this needed? We used a "full" Core i7 of the last two generations for the purity of the experiment, testing it with support enabled and disabled hyper-threading technology, because for a year and a half now, Core i5 has been supplied not with 8, but with 6 MiB L3. It is clear that the effect of cache memory capacity on performance is not as great as it is sometimes believed, but it is there, and there is no getting away from it. In addition, Core i5 are more mass-produced products than Core i7, and in the first generation, no one “offended” them in this parameter. But before they were slightly limited differently: the UnCore clock speed in the first generation i5 was only 2.13 GHz, so our "Nehalem" is not exactly a representative of the 700th line at 2.4 GHz, but a slightly faster processor . However, we considered it unnecessary to greatly expand the list of participants and rework the testing conditions - anyway, as we have warned more than once, testing this line does not bring any new practical information: real processors work in completely different modes. But for those who want to thoroughly understand all the subtle points, it seems to us, such testing will be interesting.

Test stand configuration

We decided to limit ourselves to only four processors, and there will be two main participants: both quad-core Ivy Bridge, but with different L3 cache capacities. The third is "Nehalem HT": last time it was almost identical to "Ivy Bridge is simple" in terms of the final score. And “just Nehalem” which, as we have already said, is slightly faster than the real Core i5 of the first generation, operating at a frequency of 2.4 GHz (due to the fact that the UnCore frequency was slightly lower in the 700th line), but not too radical. But the comparison is also interesting: on the one hand, there are two steps to improve the microarchitecture, on the other hand, the cache memory is limited. A priori, it can be assumed that the first will outweigh in most cases, but how much and in general - how the “first” and “third” i5s are comparable (adjusted for the UnCore frequency, of course, although if there are many people who want to see an absolutely accurate comparison, we will let's do) - already good topic for research.

Testing

Traditionally, we divide all tests into a number of groups and show the average result for a group of tests/applications on the diagrams (for details on the testing methodology, see a separate article). The results on the diagrams are given in points, for 100 points the performance of the reference test system site sample 2011. It is based on AMD processor Athlon II X4 620, but the amount of memory (8 GB) and video card () are standard for all tests of the "main line" and can only be changed as part of special studies. For those who are more interested detailed information, again, traditionally, it is proposed to download a table in Microsoft Excel format, in which all the results are given both in converted points and in "natural" form.

Interactive work in 3D packages

There is some effect of cache memory capacity, but it is less than 1%. Accordingly, both Ivy Bridges can be considered identical to each other, but the architecture improvements allow the new Core i5 to easily overtake the old Core i7 in the same way as the new Core i7 do.

Final rendering of 3D scenes

In this case, of course, no improvements can compensate for the increase in the number of processed threads, but today the most important thing for us is not this, but complete absence impact of cache capacity on performance. Here Celeron and Pentium, as we have already established, are different processors, so rendering programs are sensitive to L3 capacity, but only when the latter is not enough. And 6 MiB for four cores, as we see, is quite enough.

Packing and unpacking

Naturally, these tasks are susceptible to the capacity of the cache, but here the effect of increasing it from 6 to 8 MiB is quite modest: about 3.6%. More interesting, in fact, is the comparison with the first generation - architectural improvements allow the new i5 to “smash” even the old i7 at equal frequencies, but this is in the overall standings: due to the fact that two out of four tests are single-threaded, and one is double-threaded. Data compression by 7-Zip is naturally the fastest on Nehalem HT: eight streams are always faster than four of comparable performance. But if we limit ourselves to only four, then our “Ivy Bridge 6M” loses not only to its progenitor, but also to the old Nehalem: microarchitecture improvements completely give in to a decrease in cache memory capacity.

Audio encoding

Somewhat unexpected was not the size of the difference between the two Ivy Bridges, but the fact that it exists at all. The truth is so cheap that it can also be attributed to the features of rounding or measurement errors.

Compilation

Threads are important, but so is cache capacity. However, as usual, not too much - about 1.5%. A comparison with the first generation Core with Hyper-Threading disabled is more interesting: the new Core i5 wins even at an equal frequency, but one of the three compilers (by Microsoft, to be precise) worked on both processors in the same time. Even with a 5 second advantage for the older one - despite the fact that in this program, the "full cache" Ivy Bridge results in 4 seconds better than Nehalem. In general, here it cannot be considered that the decrease in L3 capacity somehow greatly affected the second and third generation Core i5, but there are nuances.

Mathematical and engineering calculations

Again, less than 1% difference with the "older" crystal and again a convincing victory over the first generation in all its forms. Which is more of a rule than an exception for such low-threaded tests, but why not make sure of it once again? Especially in such a refined form, when (unlike tests in normal mode) does not interfere with the difference in frequencies ("standard" or appearing due to the operation of Turbo Boost).

Raster graphics

But even with a more complete utilization of multithreading, the picture does not always change. And the capacity of the cache memory does not give anything at all.

Vector graphics

And here it is similar. True, only a couple of computation threads are needed.

Video encoding

Unlike this group, where, nevertheless, even Hyper-Threading does not allow Nehalem to fight on equal terms with followers of newer generations. But they are not too hindered by a decrease in the capacity of the cache memory. More precisely, it practically does not interfere at all, since the difference is again less than 1%.

Office software

As expected, there is no performance gain from increasing the cache capacity (more precisely, its drop from reducing it). Although if you look at the detailed results, you can see that the only multi-threaded test in this group (namely, OCR in FineReader) is about 1.5% faster at 8 MiB L3 than at 6 MiB. It would seem - what is 1.5%? Practically speaking, nothing. But from a research point of view, it is already interesting: as you can see, it is multi-threaded tests that most often lack cache memory. As a result, the difference (albeit small) is sometimes even where it should not be. Although there is nothing so inexplicable in this - roughly speaking, in low-threaded tests we have 3-6 MiB per thread, but in multi-threaded tests we get 1.5 MiB. The first is a lot, but the second may not be quite enough.

Java

However, the Java machine does not agree with this assessment, but this is also understandable: as we have already written more than once, it is very well optimized not for x86 processors at all, but for phones and coffee makers, where there can be many cores, but here is the cache very little memory. And sometimes there are few cores and cache memory - expensive resources both in terms of die area and power consumption. And, if something can be done with cores and megahertz, then with the cache everything is more difficult: in the quad-core Tegra 3, for example, it is only 1 MiB. It is clear that the JVM can “grunt” even more (like all systems with bytecode), which we have already seen comparing Celeron and Pentium, but more than 1.5 MiB per thread, if it can come in handy, then not in those tasks, which are included in SPECjvm 2008.

Games

We had high hopes for games, because they often turn out to be more demanding than even archivers in terms of cache memory capacity. But it happens when it is very small, and 6 MiB - as we see, is enough. And, again, processors of the quad-core Core level of any generation, even at a frequency of 2.4 GHz, are too powerful a solution for the gaming applications used, so they will obviously not be the bottleneck, but other system components. Therefore, we decided to shake off the dust from modes with low graphics quality - it is clear that for such systems it is too synthetic, but we have all synthetic testing :)

When all sorts of video cards and so on do not interfere, the difference between two Ivy Bridges already reaches “insane” 3%: in this case, you can ignore it in practice, but for theory it’s a lot. More came out just only in the archivers.

Multitasking environment

Somewhere we have already seen this. Well, yes - when we tested six-core processors under LGA2011. And now the situation repeats itself: the load is multi-threaded, some of the programs used are “greedy” to the cache memory, but its increase only reduces the average performance. How can this be explained? Unless the fact that arbitrage becomes more complicated and the number of misses increases. Moreover, we note that this happens only when the capacity of L3 is relatively large and there are at least four simultaneously working computation threads - in the budget segment, a completely different picture. In any case, as our recent testing of Pentium and Celeron showed, for dual-core processors, increasing L3 from 2 to 3 MiB adds 6% to performance. But four- and six-core does not give, to put it mildly, nothing. Even less than nothing.

Total

A logical overall result: since no significant difference was found anywhere between processors with different L3 sizes, there is none in the "general and whole" either. Thus, there is no reason to be upset about the decrease in cache memory capacity in the second and third generation Core i5 - the predecessors of the first generation are not competitors anyway. Yes, and the old Core i7, on average, also demonstrate only a similar level of performance (of course, mainly due to the lag in low-threaded applications - and there are scenarios that they can handle faster under equal conditions). But, as we have already said, in practice, real processors are far from equal in terms of frequencies, so the practical difference between generations is greater than can be obtained in such studies.

Only one question remains open: we had to greatly reduce clock frequency to ensure equality of conditions with the first generation Core, but will the observed patterns persist in conditions closer to reality? After all, the fact that four low-speed computing threads do not see the difference between 6 and 8 MiB of cache memory does not mean that it will not be detected in the case of four high-speed ones. True, the opposite does not follow, so in order to finally close the topic of theoretical research, we need one more laboratory work which we will deal with next time.