why do all drives have less space than actually said?

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i have seen drives like a 2tb on that i have but it only has 1.81 tb. i have a 512gb one and it only has like 495gb. why is this?

edit: typo

In: Technology

It’s a matter of marketing. One gigabyte is equal to 1024 MB to a computer, but manufacturers advertise 1 GB as 1000 MB. Because of this, a hard drive advertised being able to store 500 GB can only actually store around 490 GB on your computer.

It is due to a difference in what people actually mean when they say things like GB, TB etc

The problems comes from the fact that computers internally work binary and that a round number for computers are powers of two like 4, 8 ,16 ,32 ,64, 128, 256, 512, 1024 and so on.

Once computers started becoming big enough that you regularly had to talk about thousands of bytes, engineers wanted a word to talk about that.

As engineers they knew about the way the metric system had prefixes like kilo- to mean 1000 for kilometer, kilogram, kilowatt etc

However using kilobyte to mean 1000 byte would have been inelegant.

For example 65536 Byte is a perfectly round number but expressing it as 66 kilobyte rounded up would be inexact and saying 65.536 kilobyte would be exact but not actually any shorter.

So they used the fact that 1024 was 2^10 and really close to 1000.

They decided to define a kilobyte as 1024 byte.

This made a number like 65536 byte exactly 64 Kilobyte.

As computers got bigger this was extended to megabyte, gigabyte terabyte etc.

However the people in charge of the metric system didn’t like how they used their terms to mean something different and suggested that kilobyte should be 1000 byte and some other term like kibibyte should be used for the 1024 byte value.

Since the term was silly nobody used it initially

However makes of harddrives realized that an official standards body had given them an opportunity.

They could advertised the size of the drives in the units the metric people had suggested with a tiny asterisk and a helpful clarification at the bottom and people would think it meant a bigger value than it actually did.

Since Operating system still displayed the value in the original 1024 based units when they were advertised in the 1000 based units, people often found themselves with less space than they thought they had paid for.

It just is a dirty advertising trick.

Many of the same companies that make or sell harddrives in the 1000 byte units also make RAM and advertise those in 1024 based units. None of them sell 4.3 Gigabyte memory sticks, they advertise them as 4 Gigabyte.

It is just that you can make harddrives in size other than direct powers of 2, while RAM usually only comes in powers of 2. So they use the ambiguity to inflate the perceived size of their harddrives but leave well enough alone for other stuff.

There’s some space taken up by the file system to record what files are where. So it’ll always be less than advertised. But if you’re actually seeing 17BG gone, that might be a problem.