When you plug a brand new memory stick into your PC, it’s likely to show less capacity than it says on the box. Does this mean it’s some knockoff that’s going to corrupt your data or is it the system taking up all that extra space? Whilst both explanations are a possibility, the large discrepancy you see – whether it’s a 2GB memory stick or a 6TB hard drive – is all down to different people counting the size in a different way.
Computers work in binary, of which there are two values: 0 or 1. Due to this, when kilobytes were first termed it was for 1024 bytes and then a megabyte was 1024 KB and a gigabyte was… 1024 MB. With this way of counting a 2GB memory stick would be 2,147,483,648 bytes. However, as humans we’re much more used to counting in base10, so a kilo generally means 1000, for example 1 kilometer is 1000m. It’s this discrepancy that causes the lower capacity to appear.
When we look at a 6TB hard drive (that Windows lists as 5.45 TB) we see:
It shows very nearly 6,000,000,000,000 bytes which with the standard way of using the prefix tera would be 6 terabytes. However, if we divide that number by 1024 we get 5,859,375,000KB. Divide by 1024 again equals 5,722,046MB. Dividing by 1024 twice more gives us 5,587GB and then the 5.45TB that Windows views as 6 trillion bytes.
So those 6 trillion bytes counted one way equals 6 terabytes which is the way storage manufacturers count. OS programmers use the binary version of kilobytes which means those 6 trillion bytes equal 5.45 terabytes.
The confusion between the two versions of kilobyte led to the creation of new prefixes to denote the binary version. Kibibyte (KiB) is the correct terminology for 1024 bytes. Kibi being derived from the first letters of Kilo and binary. Similar words were created for the larger orders of magnitude; mebibyte (MiB), gibibyte (GiB) and tebibyte (TiB). However, these now correct terms aren’t often used and the confusion still remains.
Safe to say, you’ve probably not bought a knock-off USB stick, it’s just different people counting in different ways.