I just bought a ASUS Sabertooth 990FX TUF Series Motherboard which says it supports memory "4 x DIMM Max. 32GB DDR3" but when I look into its manual, none of the supported memory modules say anything with 8GB x 4, just other configurations like e.g. 4 GB x 2. My math might be wrong, but I'd think that 32 GB means it should be able to support 8GB x 4. So what does "4 x DIMM Max. 32GB DDR3" really mean? Does it mean it should be able to support 8GB DIMMs?
This means your motherboard accepts up to 32GB of memory. The BIOS is designed to allow up to 32GB, but has not been formally tested for this amount of memory.
If you are running Windows, make sure you are running Windows 7 Professional or Ultimate 64-bit (Home Premium can only accept 16GB), and as C2940680 noted, you may want to disable or manually limit the size of the pagefile, as it will be very large by default. Recent Linux kernels should have no trouble accessing this amount of memory.
Your motherboard will allow you to use UP TO 32GB RAM. However, your BIOS and OS will determine the true usability. Make sure you have latest BIOS update, and you have 64-bit OS (Windows 7-64bit, or *NUX x86_64).
For Linux, try something that will work out of ox, like Mint/Ubuntu or Knoppix, or especially kernel 3.2 and above.
You could scale down to 16GB RAM if your PC never uses more than 4GB. Remember, for Windows, you will create 32*1.5 = 48GB PAGEFILE.SYS. To prevent that, DISABLE PAGEFILE.
Hope this helps.