Why Windows can indicate a smaller displayed capacity

A difference in displayed capacity can relate to the following reasons: 

Misinterpretation of units

Size labelling on operating systems are historically indicated using binary system values, which can be confusing, and are often associated with misinterpreting capacity.

Disk manufacturers calculate using the principle:
1kB = 1000B, 1MB = 1000kB, 1GB = 1000MB, 1TB = 1000GB

Operating Systems (including Microsoft Windows) are calculated differently:
1kB = 1024B, 1MB = 1024kB, 1GB = 1024MB, 1TB = 1024GB

According to current standards however, the correct calculation for both disk manufacturers and operating systems should be in KiB units (analogue, MiB,GiB,TiB).

Example:
Box indicates a disk capacity of 1500GB (15000*1000*1000*1000B), when in most programs, the capacity will be listed as 1500*1000*1000*1000/1024/1024/1024=1396GiB. It is therefore easy to incorrectly interpret capacity.

Reserved memory for additional services

During production, most manufacturers create a hidden partition in the memory, which is later used for additional services such as backup and encryption. It is possible to cancel partitions without losing your warranty, although additional services will no longer function after cancellation.