AMD Zen 4 architecture overview. Before the storm


The AM4 platform has become probably the most successful in the entire history of the AMD company. For five years, users could not change the motherboard and constantly stay in line, enjoying the annual update of the Zen architecture. No, it’s not just three letters, it’s a generation of processor architectures that literally made the entire silicon market “stir.” The Zen architecture was the first to conquer new technological norms of production and the first to impress the world with the number of cores for the desktop segment.

AMD Zen 4

We finally saw a decent competition for the products of the blue giant and a serious growth of IPC. Now we are witnessing a new era that is hidden under the code word AM5. It is designed to continue the path of the Zen architecture and in the near future surprise users again not only with the number of cores, but also with overcoming the psychological barrier of 5 GHz for multi-threaded tasks. Agree, intriguing.

AM5 platform

Often with the release of new platforms, users ask the question “why change the socket or chipset?”, if, it would seem, we already have powerful enough power subsystems, high-quality signal line tracing and sufficient memory for UEFI. Let’s understand sequentially using the example of AM5.

AMD Zen 4

In 2022, the race for energy efficiency technologies has reached its peak, aiming to achieve maximum performance and adaptability to the type of load. Behind the screen of these beautiful words is a simpler concept – a reasonable change in frequency relative to voltage and load. In addition to the processor, the lion’s share of responsibility for this is borne by the motherboard, which must provide the requested power supply with the appropriate response. In addition to feedback, an important element is the accuracy of data received from various sensors that monitor the state of the “health” of the processor and provide it with more accurate information about the current capabilities of various VRM regulators.

AMD Zen 4

AM5 has received AMD’s new high-speed Serial Voltage 3 (SVI3) standard, previously introduced in the Ryzen 6000 series of mobile processors. SVI3 provides more accurate power management, improved telemetry control and significantly faster response to voltage changes. In particular, for desktop solutions, SVI3 also supports a larger number of power phases, which will be especially useful for high-end X670E motherboards.

The next important innovation is the PCI Express 5.0 standard. One of the main differences between each generation of PCIe is speed and bandwidth. In the language of numbers, PCIe Gen 5.0 in x16 configuration has a transfer speed of up to 32 GB/s and a bandwidth of up to 128 GB/s, which is twice that of the PCIe 4.0 standard.

Another problem that PCIe 5.0 is designed to solve is the lack of power for the video card. That’s right, PCIe 5.0 will be able to provide enough power for high-end video cards. PCI-SIG claims that each pin on the main unit can support up to 9.2 A. This adds up to 55.2 A for the entire connector with a maximum supported power of 662.4 W. Taking into account the tolerances, you will get 600 W (300 W for PCIe 4.0), which is quite enough even for a greedy video card, but with one condition – the video card must also support the PCIe 5.0 standard.

AMD Zen 4

M.2 NVMe will also get performance improvements. There are already quite a few announced products that can overcome the psychological mark of reading speed of 10 GB/s.

The number of PCIe processor lines has increased from 24 to 28, 16 are allocated for video card needs, and 8 for NVMe. Additional 4 lines are intended for peripherals and new high-speed 20 and 10 Gbit/s USB ports.

AMD Zen 4

The key differences between chipsets with the “E” suffix and those without are the mandatory support for PCI Express 5.0 processor lines for the “extreme” chipset. Interestingly, but judging by the illustration above, AMD decided not to talk about it. However, availability of support will be determined by motherboard manufacturers. The B650(E) chipset will appeal to users who do not need such a large number of ports and interfaces, which in turn will significantly save money.

AMD Zen 4

I also want to note that now the AM5 platform supports image output through USB ports of the Type-C standard, the number of which is three (!). There is also support for WiFI-E6 with DBS/Bluetooth Low Energy 5.2.

Support for high-quality DDR5 memory completes the list of unique innovations. The difference between the new RAM and its predecessor is a doubled data transfer rate. The new memory modules assume twice the number of bank groups (8 vs. 4), and the number of bank groups remains the same at four.

AMD Zen 4

As a result, the faster data bus will fill up more quickly, potentially increasing transaction efficiency, as the growing number of bank groups allows more pages to be kept open at the same time, thereby increasing the likelihood of data access. Increasing the frequency of the memory interface is provided by doubling the length of the packets. If for DDR4 one packet included eight serial transfers on the data bus, then for DDR5 there were 16 of them.

The width of the bus in both versions of RAM is the same, 64 bits, DDR5 boasts an improved channel architecture. Each strip of RAM contains two channels, not one like DDR4. The benefit of such an innovation allows you to perform two different operations simultaneously from one module. Also, each sub-channel received its own 8-bit ECC bus. This automatic error correction feature allows systems using DDR5 memory to have higher stability and no interruptions due to errors.

AMD Zen 4

The increase in the performance of DDR5 compared to DDR4 is also due to the fact that the novelty has learned to “regenerate” information in the cells bank by bank, previously this operation was carried out for all banks at once. Saving data in the cells requires regeneration of the charge after certain time intervals. In DDR4, this process required any other operations to stop, effectively blocking any useful operations periodically. In the new memory, regeneration for different banks in groups can be performed in turn, with other banks remaining available for access. This approach increases the performance of DDR5 by an additional 6-9%.

AMD Zen 4

Also, in DDR5, power management is transferred from the motherboard to the module itself (DIMM). The modules are equipped with 12-volt power management ICs (PMICs), which will allow better control of system power consumption. The PMIC also provides improved signal integrity and lower noise.

The last change is something you probably already know, DDR5 is big and a 16GB module is becoming the recommended starting point for any system.

AMD Zen 4

Summing up this section, I would like to note that the new processor architecture simply could not be implemented on the old platform, there are not just a lot of innovations, but a lot. The AM5 platform should once again become a long-lived one, support is planned until at least 2025. A nice bonus is the support for cooling systems with an AM4 mount. The only, perhaps, drawback among the above will be the price.


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