Computer - Number System

When we type some letters or words, the computer translates them in numbers as computers can understand only numbers.
A computer can understand positional number system where there are only a few symbols called digits and these symbols represent different values depending on the position they occupy in the number.
A value of each digit in a number can be determined using

• The digit
• The position of the digit in the number
• The base of the number system (where base is defined as the total number of digits available in the number system).

Decimal Number System

The number system that we use in our day-to-day life is the decimal number system. Decimal number system has base 10 as it uses 10 digits from 0 to 9. In decimal number system, the successive positions to the left of the decimal point represent units, tens, hundreds, thousands and so on.
Each position represents a specific power of the base (10). For example, the decimal number 1234 consists of the digit 4 in the units position, 3 in the tens position, 2 in the hundreds position, and 1 in the thousands position, and its value can be written as
(1x1000)+ (2x100)+ (3x10)+ (4xl)
(1x10³)+ (2x10²)+ (3x10¹)+ (4xl0⁰)
1000 + 200 + 30 + 1
1234
As a computer programmer or an IT professional, you should understand the following number systems which are frequently used in computers.

S.N.	Number System & Description
1	Binary Number System Base 2. Digits used: 0, 1
2	Octal Number System Base 8. Digits used: 0 to 7
4	Hexa Decimal Number System Base 16. Digits used: 0 to 9, Letters used: A- F

Binary Number System

Characteristics

• Uses two digits, 0 and 1.
• Also called base 2 number system
• Each position in a binary number represents a 0 power of the base (2). Example 2⁰
• Last position in a binary number represents a x power of the base (2). Example 2^x where x represents the last position - 1.

Example

Binary Number: 10101₂
Calculating Decimal Equivalent:

Step	Binary Number	Decimal Number
Step 1	101012	((1 x 24) + (0 x 23) + (1 x 22) + (0 x 21) + (1 x 20))10
Step 2	101012	(16 + 0 + 4 + 0 + 1)10
Step 3	101012	2110

Note: 10101₂ is normally written as 10101.

Octal Number System

Characteristics

• Uses eight digits, 0,1,2,3,4,5,6,7.
• Also called base 8 number system
• Each position in a octal number represents a 0 power of the base (8). Example 8⁰
• Last position in a octal number represents a x power of the base (8). Example 8^x where x represents the last position - 1.

Example

Octal Number: 12570₈
Calculating Decimal Equivalent:

Step	Octal Number	Decimal Number
Step 1	125708	((1 x 84) + (2 x 83) + (5 x 82) + (7 x 81) + (0 x 80))10
Step 2	125708	(4096 + 1024 + 320 + 56 + 0)10
Step 3	125708	549610

Note: 12570₈ is normally written as 12570.

Hexadecimal Number System

Characteristics

• Uses 10 digits and 6 letters, 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F.
• Letters represents numbers starting from 10. A = 10. B = 11, C = 12, D = 13, E = 14, F = 15.
• Also called base 16 number system
• Each position in a hexadecimal number represents a 0 power of the base (16). Example 16⁰
• Last position in a hexadecimal number represents a x power of the base (16). Example 16^x where x represents the last position - 1.

Example

Hexadecimal Number: 19FDE₁₆
Calculating Decimal Equivalent:

Step	Binary Number	Decimal Number
Step 1	19FDE16	((1 x 164) + (9 x 163) + (F x 162) + (D x 161) + (E x 160))10
Step 2	19FDE16	((1 x 164) + (9 x 163) + (15 x 162) + (13 x 161) + (14 x 160))10
Step 3	19FDE16	(65536+ 36864 + 3840 + 208 + 14)10
Step 4	19FDE16	10646210

Note: 19FDE₁₆ is normally written as 19FDE.