Random Access Memory or RAM is an essential component of your computer and it helps your devices perform faster and better. However, if the RAM is not running at full speed, it can lead to various problems like slowdowns or crashes.
There are three main reasons why your ram not running at full speed and motherboard incompatibility is one of them. Some motherboards simply do not support the maximum RAM speeds that the motherboard and CPU can handle. This means that if you buy a DDR4 RAM kit with advertised speeds of 4000 MHz, your system will only run at the minimum standard speed (pretty much always 2133 MHz).
Another reason why your ram not running at full speed is because it is not enabled or set to its default settings. Most modern computers should automatically detect new memory and set its timings based on a JEDEC-approved SPD table. Unfortunately, it doesn't always work that way. For example, I bought some 3600 MHz RAM and when I ran inspection utility apps like Speccy or CPU-Z, both showed that it was only running at 1799.6 MHz!
To fix this, open the BIOS and look for the "RAM speed" setting. Make sure that it matches the advertised speed of your RAM stick(s). If you're an advanced user, you can also enable XMP through your laptop UEFI to get even more performance out of your ram. In any case, this should solve your ram not running at full speed problem and you'll be able to enjoy the full performance of your RAM.