Why 1 megabytes is 1024 instead of 1000

Answer 1

https://en.m.wikipedia.org/wiki/Megabyte#Definitions

Answer 2

Because in computers, the system that is really used is binary.

And, in binary, the exponentiation sequence goes like this:

2⁰ = 1
2¹ = 2
2² = 4
2³ = 8
2⁴ = 16
2⁵ = 32
2⁶ = 64
2⁷ = 128
2⁸ = 256
2⁹ = 512
2 ^ 10 = 1024