AMD is reportedly gearing up to bring 3D V-Cache technology to its Zen 4 mobile CPUs, and the time has finally come. Chips with V-Cache have been available in desktop and server form for a long time, but until now there has been no example of the technology being built into AMD Mobile’s chips.
According to the tweet of (X or something) @9550pro, the first chip is the Ryzen 9 7945HX3D. This will be featured in the upcoming Asus ROG Scar notebooks. The chip features 16 Zen 4 cores and a total of 128MB of L3 cache. This consists of 32MB for each of the two chiplets, plus an additional 64MB of stack cache.
As this chip sits at the top of AMD’s mobile CPU line, we can expect it to find its way into flagship desktop replacement machines with top-of-the-line GPUs. Battery life and mobility are not the selling points of these systems. Performance is what counts, and it’s entirely possible that notebooks with this chip will be the fastest on the market.
If the mobile V-Cache chip proves to be a success for AMD, there’s no reason to doubt that the technology will gradually seep into models around the world. Chips with 8-core or 6-core V-Cache should offer good gaming performance. If you’re lucky, the price won’t be too high and you’ll get the long battery life that AMD’s mobile CPUs are known for.
I’m surprised AMD doesn’t release a V-Cache model for the notebook market. Considering the characteristics of the mobile chip, it is a natural fit. Without his TDP or thermal budget of a desktop chip and with lower clocks, more L3 cache should be an added advantage for games that need power-hungry raw clock speeds to maximize performance.
The default TDP of the Ryzen 9 7945HX without V-Cache is 55-75W. This means there is no concern about the brittle nature of the TSV interconnect that links chiplets and caches. Excessive voltage is the enemy of V-Cache, but it’s fine for low-voltage mobile chips.
How successful these chips are depends on the rest of the system. The V-cache model won’t magically speed up GPU-limited games running at 4K, but it can help at lower resolutions on systems with very high refresh rate screens. A system with a 7945HX3D, RTX 4090 and 1080p screen is unlikely to be released, but a high-end GPU capable of 240+ FPS at 1440p is possible. A well-optimized eSports game is a good example, and the X3D mobile chip should perform best in such use cases.
Of course, not all games and applications benefit from stacked caches. Some benefit from more clock speed, but the system still has to fall back to system memory when the L3 cache is full. It will be interesting to see how AMD tweaks turbo modes, chiplet software and drivers to provide optimal performance for all types of mobile workloads.