Why are storage mediums advertised at higher capacities than what they actually are?

Question

I have two SSD hard drives. Both are advertised as 240Gb capacities. Meanwhile, Windows shows them as only having ~222Gbs. I see this trend across different storage mediums like flash drives as well.

Why?

Answer 1

It's Windows, not the SSD.

When Windows says the disk has 222GBs free, it means the disk has 222GiBs free. 222GiBs is approximately equal to 238GB.

222 * 1024 * 1024 * 1024 / 1000000000 = 238.37

Largely for historical reasons, operating systems traditionally report sizes in power of 2 units but use the nomenclature for power of 10 units.

Answer 2

Formatting takes up space. Also the rated capacities are base 10 (1000) while computer uses base 2 (1024). So because of the base difference and formatting; storage capacity is always less than rated capacity

Answer 3

This is neither a new trend nor overly misleading and there are two traditional reasons:

1. As touched on already, there are two definitions of a GB. A MB is 1KB x 1KB. A GB is 1KB x 1MB or 1KB x 1KB x 1KB. To a computer scientist, 1K is 1024. To marketing people, 1K is 1000. So, Marketers consider 1Meg to be 1,000,000,000 while us geeks consider it to be 1,073,741,824 giving you a discrepancy of how big a capacity a device actually has.

2. An "empty" device is not empty and does not have 100% of its space free. Some of the device must be reserved for containing the file structure and information on what parts of the device is available for use, and what is in use. This information consumes a part of the space which is included in the total capacity but will never be available as free space for your use.