When it comes to buying a hard drive, most people tend to look only at the capacity specified in the product description. For example, a 1 Terabyte (TB) hard drive seems like a lot of storage space, right? However, when you plug that hard drive into your computer, you may be shocked to find that it only shows up as having around 931 Gigabytes (GB) of available space.

So, why is this the case? Why do hard drives have less actual space than what is advertised?

The answer lies in the way computer storage is measured. To understand the concept, we need to look at the difference between decimal and binary numbering systems.

In the decimal system, we use ten digits (0-9) to express numbers. Therefore, when we say “1”, it equates to one unit. However, computers use the binary system, which only has two digits (0 and 1). In this system, one unit equals to “2^1,” which is 2. The larger the number gets, the more significant the difference becomes.

Hard drive manufacturers use decimal numbers to measure the capacity of their drives, while computers utilize binary numbers. Therefore, when a hard drive manufacturer advertises a product as having 1 TB of storage space, they’re using the SI (International System of Units) definition, where “Tera” means 10^12 bytes.

However, a computer’s operating system will read the drive’s capacity using binary numbering. According to the binary system, a TB equals 2^40 (1,099,511,627,776) bytes. When this is converted to Gigabytes, we get approximately 931 GB.

So, the difference between an advertised capacity of 1 TB and the actual available space of approximately 931 GB boils down to the difference between the two numbering systems.

It’s not just hard drives; this difference in measurement applies to any storage device, including USB flash drives and Solid-State Drives (SSD).

It’s worth mentioning that hard drive manufacturers are not attempting to mislead buyers. The discrepancy in capacity measurement is due to standardized practices in the industry and the realities of the technology that cannot be changed overnight.