In a surprising turn of events, AMD might not allow any overclocking on its soon-to-launch Ryzen 7 5800X3D CPU. This is AMD’s first consumer CPU with a huge 64MB chunk of on-die 3D L3 cache. This gives the CPU a total of 96MB of L3 including the 32MB included in the base chiplet. Though no official explanation has been given, Techpowerup has confirmed the situation via its own sources. It’s not clear if this is a final decision, but the CPU is close to launch. It’s late in the game for a UEFI modification like this to be a temporary measure.
Word of the apparent lack of overclocking support for the 5800X3D first came from a post on Chinese social media platform Bilibili, with a user posting a blurred-out photo of the CPU with the IHS attached. The same post notes that “so far” the chip does not allow overclocking. Techpowerup says it has verified this rumor by reaching out to companies that make AMD motherboards. According to their sources, what AMD told these manufacturers is as follows, “5800X3D 8C16T 100-xxxxxxxxx 105 W AGESA: PI 1206b 1/28 Please hide Vermeer-X CPU OC BIOS SETUP options.” AGESA 1.2.0.6 B is the latest BIOS for AMD motherboards. It is just now rolling out for most AMD64 motherboards and some manufacturers are labeling it as a beta build. Future changes are therefore possible.
News of this alleged limitation isn’t too much of a shocker. Not only is there precedent for this, AMD’s CPUs aren’t exactly known for offering a lot of overclocking headroom to begin with. In general cache frequencies are known to not scale very well with CPU clock frequencies, which is why both Intel and AMD have previously allowed L3 cache to be overclocked separately from the main CPU core.
In addition to intrinsic clock speed issues, there might also be thermal issues at play here as well. The V-cache is also half the size of the chiplet below it, so there is also potential for heat buildup in a very small area, with a hot CPU die directly below it. AMD has said that it placed the vertical L3 in an area of the die where it would not particularly impact heat transfer, but there’s inevitably going to be at least some additional heat generation. For both of these reasons, it makes sense for AMD to keep a tight lid on the CPU’s operating specs.
As a bit of a refresher, the Ryzen 7 5800X3D is an upgraded version of the existing 5800X that is aimed at the gamers. It’s extra L3 cache is probably a toe in the water as AMD is likely to use similar technology in its upcoming Zen 4 CPUs. The 5800X3D has a single eight-core chiplet with base/boost clocks of 3.4GHz and 4.5GHz, slightly lower than the 5800X’s 3.8GHz and 4.7GHz clocks.
Interestingly when the company first demonstrated its 3D stacking technology on a CPU last year at Computex, it was on a two-chiplet 5900X CPU. That might have been a bridge too far as it just settled on a single chiplet CPU for the official product. The Ryzen 5800X3D should be launching soon at a rumored MSRP of $449, which is the same price as the OG Ryzen 7 5800X.
https://www.extremetech.com/computing/332586-amds-v-cache-boosted-ryzen-7-5800x3d-might-not-allow-ov...
