In what form do the hexadecimal numbers need to be converted for a computer's digital circuit to process them?

Hexadecimal numbers are just a convenient representation of binary data. When entered as text, they consist of ASCII characters 0-9 and a-f. The numbers will then have to be converted to binary. This is accomplished by converting to uppercase, subtracting the ASCII offset (48 for 0-9 or 55 for A-F), so that the result is a number between 0 and 15 (inclusive). This can be stored in computer memory to represent 4 bits.

Hexadecimal numbers represent binary numbers in the following way:

hex | binary

0 = 0000

1 = 0001

2 = 0010

3 = 0011

4 = 0100

5 = 0101

6 = 0110

7 = 0111

8 = 1000

9 = 1001

a = 1010

b = 1011

c = 1100

d = 1101

e = 1110

f = 1111

As you can see, no other 4 bit combination exists.