While digging into the motherboard’s settings it is common to see the Above 4G Decoding option and by default, it is disabled.
If you are thinking that at the consumer level you’ll get any benefit of enabling Above 4G Decoding then be alert there because it won’t.
So what the heck is Above 4G Decoding?
Above 4G Decoding is to allow the user to enable or disable memory-mapped I/O for a 64-bit PCIe device to 4GB or greater address space.
In layman’s term, Above 4G Decoding, when enabled, allows 64-bit PCIe devices to use addresses in the 64-bit address space.
Since 32-bit operating systems cannot access the 64-bit address space (32-bit processor, or a processor in 32-bit mode, can access 232 Bytes, which is 22×230 = 4 GiB or 4 GibiBytes).
When should I enable Above 4G Decoding?
Generally, we enable it when one has many PCIe cards installed, such as with Quad SLI and using GPGPU (General Purpose Graphics Processing Unit) compute modules such as NVIDIA’s Tesla. Please enable this feature when using multiple graphics cards for cryptocurrency mining. Above 4G Decoding is also useful in a mining rig, because while mining cryptocurrencies you’ll definitely need larger address space as the difficulty level could increase afterward.
It’s more commonly used in workstations and servers.
Since neither setting should cause issues on a 64-bit operating system, you can enable or disable it without any ill effect most of the time.
Just with a GPU card, you would definitely NOT need to enable this.