Of course everyone knows that 1 Kilobyte equals to 1.024 bytes. Well - this is wrong !

A kibibit (a contraction of kilo binary digit) is a unit of information or computer storage, abbreviated Kibit, or sometimes Kib. (Note that the abbreviation is capitalized, while kbit is not.)

1 kibibit = 2¹⁰ bits = 1,024 bits
1 kibibit = 2⁷ bytes = 128 bytes

The kibibit is closely related to the kilobit, which can either be a synonym for kibibit, or refer to 103 bits = 1,000 bits, depending on context.
The National Institute of Science and Technologies notes that

it is important to recognize that the new prefixes for binary multiples are not part of the International System of Units (SI), the modern metric system.

It should also be noted that they are not in general use among professional software and electrical engineers, who generally use decimal prefixes when referring to binary quantities.

In short - we need to make the difference between the Metric Prefix system - this one handles the comon Kilo naming convention, and the Binary prefix systems - which is the real definition for binary formats as found on harddisks.

The following table shows you the comon namings and sizes

BTW - same also applies to the Byte fraction

By looking at these 2 previous tables - you might ask yourself - but what is the difference. Well - really only if you handle Bytes or Bits. This is the main differenciator.
So - what does this mean for us ? Check for yourself with some examples: