Question:
How many bytes are in a kilobyte?  and how many kilobytes in a megabyte.

Answer:
Many people think that there are 1000 bytes in a kilobyte. After all, "kilo" means 1000. In most cases, this approximation is fine for determining how much space a file takes up or how much disk space you have.

But there are really 1024 bytes in a kilobyte. The reason for this is because computers are based on the binary system. That means hard drives and memory are measured in powers of 2. For example:
2⁰ = 1
2¹ = 2
2² = 4
2³ = 8
2⁴ = 16
2⁵ = 32
2⁶ = 64
2⁷ = 128
2⁸ = 256
2⁹ = 512
2¹⁰ = 1024
Notice how 2¹⁰ is 1024. Therefore, 2¹⁰, or 1024 bytes compose one kilobyte. Furthermore, 1024 kilobytes compose one megabyte, and 1024 megabytes compose one gigabyte. For most practical purposes, you can estimate 1024 to 1000.