In modern motherboards BIOS, you can find the Above 4G Decoding checkbox, and now the Resizable Bar has appeared next to it. And the Resizable Bar was already well explained by AMD – the processor can directly communicate with the card through a couple of big steps, instead of a million tiny ones.
But what then is Above 4G Decoding and is it equal to Resizable Bar? No article on the internet explains the term precisely, but I will try to make the best explanation possible.
You may have noticed that a video card looks like a separate computer inside a computer. These devices have their own BIOS, a separate set of memory, their own power circuits and, of course, their own processor, even it called GPU, not CPU. It is easy to guess that they have similar and different features with the central processor, but they need to communicate: it is the central processor that commands the video card.
Therefore, for interaction, the processor often places copies or a cache of data in RAM to work with a video card. Then it transfers such information to the card via the PCI bus. Usually, the area for storing such information was limited to the first 4 Gigabytes of RAM.
And since modern software, operating systems and processors began to work with 64-bits, then much more space must be managed. And after 32-bit, where there was a limit of only 4 Gigabytes of data, now hardware and software can handle much larger values at the same time (in theory, up to 16 Exabytes, in existing hardware implementations there are only 256 Terabytes).
Judging by the reviews, it is not worth fixing what is not broken: some users have problems when this option is enabled. However, owners of cards with more than 4GB of memory, or with more than 16GB of RAM in the system, can try this function for better performance of computing tasks. Before that, many recommend updating the drivers and BIOS.
For example, scientific computing on Tesla cards, rendering large scenes for 3D artists, or mining modern cryptocurrencies will require more than 4 gigabytes of data at a time to be used effectively.
Previously, the task was solved by a queue of intermediate operations in the drivers and the system so it never exceeds the allocated 4 Gigabytes, but this reduces performance, and for some tasks, it is completely unacceptable (owners of Tesla cards or several video capture cards have faced problems for a long time).
It is worth considering that the consumption of RAM may increase at some moments, so it is rather dangerous to carry out this trick on computers with 8-12GB in modern realities.
The Above 4G Decoding checkbox is definitely required in order for the Resizable Bar to work for Radeon 6000 (RDNA2) and NVIDIA RTX 3000 (Ampere) users. Moreover, both functions can already be enabled on modern motherboards with a fresh BIOS.
What's the difference between these two technologies?
Sounds like a pretty handy combination. By the way, I was pushed to the sinful land of BIOS tuning due to investigating the mining boom. Well, at least some benefit from these good guys... miners!
Above 4G Decoding can be currently enabled on motherboards with support for AMD Ryzen 5000 processors (for example, AMD B550, X570 chipsets), and on other platforms, this feature is determined by the manufacturer.
If you do not find such a function, then you may need to update the BIOS (if support is declared in the description of the updates or from the manufacturer).
For Intel users, the feature is widely available on the Z490 chipsets, but it is also optionally found on the Z390 and even some server solutions, including relatively old ones, because the option itself was incorporated into the PCI-E standard more than 10 years ago.
