This is a common question from users especially with SSDs in particular. A 2TB SSD for example will report having 1698GB free. There are several factors to consider here:
- Hard Drive / SSD manufacturers typically show their storage capacity in GB which is understood in terms of 10^9 bytes. However, the systems work based on the binary system where a GB (or more precisely GiB) equals 2^30 bytes or 1,073,741,824 bytes. This means that 1TB is not exactly 1000 GB but, in fact, about 93% of that which is 930GB for a 1TB drive.
- The storage size does not include the system partition, which varies between 60GB and 120GB depending on the storage size.
- SSDs normally reserve some space (around 5%) for over-provisioning. This allows the SSD to work more reliable and extend durability.