There is a difference in how Hard Disk Capacities are stated by manufacturers compared to how operating systems calculate them.
To Hard disk manufacturers a kilobyte is 1000 byes, a megabyte is 1000 kilobytes , a gigabyte is 1000 megabytes and a terabyte is 1000 gigabytes = 1,000,000,000,000 bytes. However to most operating systems a kilobye is 1024* bytes, a megabyte is 1024 kilobytes (=1,048,576 bytes) and a gigabyte is 1024 megabytes (1,073,741,824 bytes), etc.
So when a hard disk manufacturer says a hard disk has a capacity of 1 Terabye it means the capacity is 1,000,000,000,000 bytes +/- a few percent. For demonstration purposes let's assume that they mean exactly 1,000,000,000,000 bytes. When the operating system calculates that capacity in Gigabytes it divides the 1,000,000,000,000 bytes by 1,073,741,824 bytes/gigabyte which equals 931.3 gigabytes.
So the reported 930 GB is about right. There is no space missing.
This difference in how hard disk capacities are stated has existed since the days when a large hard disk was only 5 MB.
* 1024 = 2^10 and is the power of 2 that is closest to 1000.