Definitions:
1)
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.
2) Base 10- It is our decimal (base-10) number system.
In our
customary base-ten system, we have digits for the numbers zero through nine. We
do not have a single-digit numeral for "ten". Yes, we write "10", but this
stands for "1
ten and 0
ones". This is two digits; we have no single solitary digit that stands
for "ten".
3) Computers use binary numbers, and therefore
use binary digits in place of decimal digits. The word bit
is a shortening of the words "Binary digIT."
4) (4*1000)+(3*100)+(2*10)+(1*1)=4000+300+2+1.
5)
Binary
form : 21(10101),
24(11100),
30(11110)
Example
of 30 : 
6)
Bits
are rarely seen alone in computers. They are almost always bundled together
into 8-bit collections, and these collections are called bytes.
7)
Bytes:
Kilobytes- 1,024
Megabytes- 1,048,576
Gigabytes- 1,073,741,824
Terabytes- 1,099,511,627,776
