What's new with the AMD Ryzen 5000 Mobile: Zen 3 on your laptop

AMD has just revealed details about the architecture of its Zen 3-based SoCs and CPUs for laptops, codenamed 'Cezanne' and known as Ryzen 5000 Mobile. What are the differences, similarities, and particularities of the Cezanne architecture compared to Vermeer for desktop PCs, how is it different from its predecessor "Renoir" and how is it similar?

Monolithic vs MCM

Despite the fact that the AMD Ryzen 5000, part of the 5000U and the 5000H are based on Zen 3. It must be taken into account that in the case of the 5000U and the 5000H we are not talking about a processor composed of several chiplets but a processor monolithic. This means that although the architecture and therefore the organization and communication of the elements are the same, in the case of SoCs and CPUs that we discuss in this article we refer to processors built on a single chip.

Core Zen 3 on AMD Ryzen 5000 Mobile

The first point is the Zen 3 core, its architecture is exactly the same as in the desktop version based on chiplets, but there is an input difference and that is that for reasons of space on the chip its cache is only 16 MB for the 8 cores, instead of being 32 MB, however, compared to its direct predecessor, Ryzen 4000 also known as "Renoir", the amount of L3 cache has increased from 1 MB per core to 2 MB per core, and a total of 8MB to 16MB.

In the case of all Zen architectures, the L3 cache serves as what we call a "Victim Cach2", this is important since it adopts the cache lines that are discarded from the L2 cache, preventing them from falling into memory and having What to rescue from there, this is important due to the fact that recovering data from memory has an energy cost that is an order of magnitude greater than in an internal memory of the processor.

The slide above these lines is illustrative of the "Victim Cache" in the Zen architectures and does not belong to the Ryzen 5000 Mobile, we clarify this in case you see confusing the 8 MB of L3 cache in it instead of the 16 MB.

At the core level, the changes that AMD has made in Zen 3 are mainly based on increasing the IPC, this has been achieved by re-making the core in such a way that there is less contention between the instructions so that the average number of instructions resolved by clock cycle increase.

Thanks to these changes, the CPU can not only achieve a higher clock speed under the same consumption as the Ryzen 4000 but also

Legacy memory controller, Northbridge and Southbridge

Outside of the Zen 3 cores, the rest of the Ryzen 5000U and Ryzen 5000H, at least in the section on communication between the different processors and accelerators with memory is exactly the same as in the Ryzen 4000U and Ryzen 4000H, which has allowed AMD to deploy its AMD Ryzen 5000 for notebooks, just months after the launch of its predecessors.

In the Ryzen 4000, however, AMD used two memory controllers for the different versions of its chips, one of them for DDR4 and the other for LPDDR4, for the Ryzen 5000 for laptops, AMD's decision has been to use LPDDR4 memory. , which can achieve the same bandwidths as DDR4 but with much lower power consumption than DDR4.

The greatest counterpart? There are no DIMMs or SO-DIMMs for LPDDR4 memory, so in most configurations, the memory will be soldered to the board. The Ryzen 5000 Mobile, like its predecessor, inheriting the same communication structure, supports up to 4 LPDDR4 memory chips.

On the other hand, AMD has also announced support for LPDDR4X memory, this variation of LPDDR4 memory has the ability to achieve the same transfer capacity with much lower voltage and therefore with less energy consumption. Its density is much higher than DDR4 and LPDDR4, although like the latter it is not sold in the form of modules.

Optimizations in the energy consumption of the Ryzen 5000 Mobile

One of the things that AMD created for Zen architecture is the fact of separating the different elements of the SoC into small "islands" or "geographical" zones. In this way AMD can turn off parts of the SoC or CPU that are not being used at all times and make sure they are not wasting power. Something that in the Ryzen 5000 Mobile AMD has done with the audio codec and the screen driver, two accelerators that are not always or partially active.

In the case of the screen controller of the second monitor, unless we connect an external monitor to the laptop, it does not make sense to use energy, the same with the audio and video codecs if, for example, we are not using them.

But the most significant change is the so-called CCPC, which consists of the Ryzen 5000 Mobile each and every one of the Zen 3 CPU cores has their own domain, this means that at certain times these cores may fluctuate their clock speed and voltage independently of each other.

Before they all went up and down in unison, but with the new system, we can find that depending on the application and the workload, not all the cores go up in the same way, unless it is necessary. So it is a way to save energy consumption and increase battery life and prevent the SoC from generating more heat than necessary.

Changes in the graphics system of the Ryzen 5000 Mobile

For the umpteenth time, AMD has once again used the AMD Vega architecture at 7nm, so RDNA architectures remain unreleased as iGPUs outside of game consoles. The main novelty? The ability to reach 2.12 GHz.

Keep in mind that AMD has spent the last few years tweaking its GPU architectures so that higher clock speeds can be achieved from the same ISA, be it RDNA, RDNA 2, GCN or CDNA. Increasing the clock speed without changing the manufacturing node means redesigning all the stages of each of the instructions, increasing the amount of these but decreasing the time per stage and thereby increasing the clock frequency.

AMD has performed this process on all of its GPUs so that they can achieve higher clock speeds under TSMC's 7nm node, whether dedicated or integrated.

Which Ryzen 5000 Mobile models are Zen 3 and which are not?

So that there are no confusion in the purchase:

• All Ryzen 5000U models whose second number is odd to use Zen 2 cores, that is 5100U, 5300U, 5500U, 5700U.
• All Ryzen 5000U models whose second number is even used Zen 2 cores, that is 5200U, 5400U, 5600U, 5800U.
• All 5000H models are Zen 3 core.

In addition, it must be added that like their predecessors, the H models have a TDP of 45 W and lack or do not have the integrated GPU active, while in the U models their TDP is 15 W and have an integrated GPU.