Clock Frequencies

The following chart shows how well the processor sustains its clock frequency and which boost clock speeds are achieved at various thread counts. This test uses a custom-coded application that mimics real-life performance—it is not a stress test like Prime95. Modern processors change their clocking behavior depending on the type of load, which is why we provide three plots with classic floating point math, SSE SIMD code, and modern AVX vector instructions. Each of the three test runs calculates the same result using the same algorithm, just with a different CPU instruction set.



Wow! The 9800X3D runs at 5.22 GHz all the time—no matter how many cores are active. This is an interesting development, usually clock speeds go down gradually as the processor load increases. It's also good to see a clock frequency that's slightly above the rated maximum boost.

Overclocking

While overclocking was disabled on previous X3D processors, this is fully supported on the 9800X3D. One important development for this ability is that AMD has now placed the 3D V-Cache tile under the CCD with the CPU cores, instead of on top of it. This improves thermals, because heat doesn't have to travel through the X3D's cache silicon anymore.

First, I tried a standard all-core CPU overclock:

• The BIOS doesn't permit a positive CPU core voltage offset, only a negative one, but it does allow setting a fixed voltage
• Maximum manual voltage is 2.0 V
• I went with 1.35 V, which was still easy to manage in terms of cooling
• The highest clock speed I reached was 5.4 GHz across all cores, but it wasn't fully stable, so I reduced it to 5.3 GHz
• As we found out earlier on this page, the processor operates at 5.22 GHz with all cores active right out of the box, so the increase to 5.3 GHz doesn't provide a significant performance gain and wastes energy because of the manual voltage setting

Next, I focused on tweaking AMD Precision Boost Overdrive (PBO):

• I removed all the power and current limits (which aren't an issue anyway)
• I also set +200 MHz with a scalar of x10
• Last but not least, I set Curve Optimizer to -10 all cores
• That turned out to be fully stable, so I set -15, -20 and -25 with quick stability testing at each setting
• At -25 the CPU was slightly unstable, so I settled for -20
• The benchmark charts include a full run at this setting (blue bar)

Additionally, I wanted to explore what's possible in terms of memory:

• Maximum SoC Voltage allowed in BIOS: 1.3 V
• DDR5-8000 is not happening on my CPU, not even with 1.3 V SoC. 7800 MT/s works, but that's not high enough to make up the loss of UCLK 1:2
• CUDIMMs with clock driver are not supported. They can run on Zen 5, but in a compatibility mode that bypasses the clock driver IC, so they behave like normal DIMMs
• At 1.3 V SoC the CPU can boot into Windows with memory running at DDR5-6400 1:1, but crashes in benchmarks
• 6200 MT/s 1:1 was easy, even at default SoC of around 1.23 V
• I included a full run with the PBO settings above, plus 6200 MT/s 1:1 at 28-36-36-72 (red bar)