How much is:

1000MB = 1 GB
500 GB = approximately 500 000 megabytes
500 KB = approximately 0.5 megabytes

how many bytes in:

a kilo this has 1000 bytes

a mega has a 1 million 

a giga has a billion 

and a terra has a 1 trillion 

What is a Byte

A byte is a group of binary digits or bits (usually eight) operated on as a unit.

Binary numbers

computers use binary numbers, and therefore use binary digits in place of decimal digits as they don'y use base 10 Therefore, a binary number is composed of only 0s and 1s

The word "bit"

The word 'bit' was derived from the term binary digit (0 and 1)

"normal" counting numbers

Digit

A digit is a single place that can hold numerical values between 0 and 9. Digits are normally 
combined together in groups to create larger numbers. For example, 6,357 has four digits. It is understood that in the number 6,357, the 7 is filling the "1s place," while the 5 is filling the 10s 
place, the 3 is filling the 100s place and the 6 is filling the 1,000s place.