German publication Igor's Lab has launched an investigation into why Nvidia chose 19 Gbps GDDR6X memory for the GeForce RTX 3080 and not the faster 21 Gbps variant. There are various claims, but it's not entirely clear how exactly some of the testing was conducted, or where the peak temperature came from.
The GeForce RTX 3080, which is the newly anointed king of gaming graphics cards, comes equipped with 10GB of GDDR6X memory. Unsurprisingly, the 10 memory chips are from Micron since the U.S. chipmaker is the only one that produces GDDR6X memory. However, some might find it intriguing that Nvidia opted for the 19 Gbps variants, when Micron currently offers 21 Gbps chips as well. Since Nvidia is Micron's only GDDR6X customer, stock shouldn't be a problem.
The research from Igor's Lab suggests that Nvidia's choice was due to thermal issues and could explain why the success rate of pushing the memory beyond 20 Gbps is pretty slim.
For reference, Micron rates its GDDR5, GDDR5X and GDDR6 memory chips with a Maximum Junction Temperature (TJ Max or Tjunction Max) of 100C (degrees Celsius). The typical recommended operating temperatures ranges between 0C to 95C. The reading materials on Micron's GDDR6X don't reveal the TJ Max for the new memory chips so there's still a bit of mystery to the topic. According to Igor, the general consent is around 120C before the GDDR6X chips suffer damage. This would mean that the Tjunction value should be set at 105C or up to 110C.
In order to prove his theory, Igor coated the backside of his GeForce RTX 3080 with a transparent substance that has an emissivity of roughly 0.95. He didn't mention the exact name of the material, but stated that it's widely use in the industry to safeguard component against environmental hazards, such as high air humidity. The reviewer kept his ambient temperature at 22C and let Witcher 3 run at 4K during 30 minutes.
At that point, he took readings of the board with his Optris PI640 thermal camera and a 'special' piece of software that's only available for internal use. That generated the above image, which is blurred out except for the mem. temp field.
According to the results, the hottest GDRR6X memory chip had a Tjunction temperature of 104C, resulting in a delta of around 20C between the chip and the bottom of the board. Another interesting discovery is that the addition of a thermal pad between the backplate and the board helps drop the board temperature by up to 4C and the Tjunction temperature around 1-2C.
Again, it's not clear how all the testing was conducted. Reading memory temperatures from underneath a heatsink is tricky in the best of situations. The takeaway is that the GDDR6X memory chips run hotter on the inside of the card than on the outside (under the backplate) due to the surrounding components, such as the voltage regulators. Even if you were to up the Tjunction to 110C, the additional 6C doesn't represent a large enough headroom before throttling kicks in. Yet another reason to ensure your PC has sufficient cooling if you're planning on running a 320W or higher TGP RTX 3080.
