Notes on Octal Number System | Grade 9 > Computer > Number System | KULLABS.COM

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#### Octal

The number with base eight is called octal number. It is represented by Q or O. We can generate these numbers with the combination of 0, 1, 2 3, 4, 5, 6, 7. We can represent these numbers wit suffix eight. Eg (5432)8

Weighted value
 85 84 83 82 81 80 32768 4096 512 64 8 1

#### Conversions from Decimal to Octal

Decimal number is repetitively divided by eight and remainders are arranged in the form of octal numbers.
Example
1. Convert (240)10into octal.

 8 240 0 8 30 6 3

(240)10= (360)8

2. Convert (356)10 into octal.

 8 356 4 8 44 4 4

(365)10=(444)8

#### Conversions from Octal to Decimal.

Each octal is multiplied by its weighted position. The sum of all products is known as decimal form of octal.
Example
Convert the octal numbers into decimal

1. (340)8= 3 x 82 + 4 x 81+ 0 x 80 =192 + 32 + 0 = (224)10
2. (175)8= 1 x 82 +7 x 81+ 5 x 80 = (125)10

#### Octal to Binary and Binary to Octal Conversions

The three digit format of binary digits is used for octal to binary conversions or vice-versa.

##### Octal to Binary

3-bits binary numbers are written for each octal digit.
Example

1. Convert (56)8 (octal) into binary.

Algorithm:

• Convert each octal digit into binary and make three digits grouping.
5= 101
6= 110
Now our equivalent binary number is (56)8=(101110)2
1. Convert (64102)8 into Binary number.
6= 110
4= 100
1= 001
0= 000
2= 010
Now our equivalent binary number is (64102)8= (110100001000010)2

##### Binary to Octal

The binary numbers are broken into 3-bits section from last bit and convert into octal equivalent of each binary section. Table shows the decimal, octal and equivalent binary bits.

 Decimal Octal Binary 0 0 000 1 1 001 2 2 010 3 3 011 4 4 100 5 5 101 6 6 110 7 7 111

Example

1. Convert (10011)2 into octal number.

Algorithm

• Make 3-bits grouping from last bit.
010 011
• Convert each group into decimal numbers.
010 = 2
011 = 3
= (23)8
1. Convert (1011010011)2 into octal number.
001 011 010 011
001= 1
011= 3
010= 2
011= 3
= (1323)8

Algorithm

• Convert octal into binary.
• make groups of 4-bits from last bit.
• convert each group into decimal numbers.

Example

• Convert into binary
3= 011, 4= 100, 7=111, 6= 110, 5=101
(011100111110101)2
• Make a four digits group from the last bit of the binary number.
0011 1001 1111 0101 (Add 0 before the group to make four digit)
3 9 15 5 (Convert into equivalent decimal numbers)
=(39F5)16 Where F= 15

• The number with base eight is called octal number. It is represented by Q or O.
• When decimal number is repetitively divided by eight and remainders are arranged in the form of octal numbers,then decimal number are converted into octal.
• Each octal is multiplied by its weighted position. The sum of all products is known as decimal form of octal.
• The three digit format of binary digits is used for octal to binary conversions or vice versa.
.

### Very Short Questions

A number system that uses eight different digits to represent different values is known as octal number system. The base of octal number system is 8 because it consist eight digits from 0 to 7. The octal number system is used in the computer to represent binary numbers. The place values in the octal number can be expressed by using powers of 8.

The procedure for conversion of octal numbers to their decimal equivalents is similar to conversion of binary numbers to their decimal equivalents but with the difference, that the base used in this case is 8 instead of 2 used in binary.

Convert (5264)8 into Decimal

Solution:

3 2 1 0 (weight)

Octal Number: 5 2 6 4

Decimal Equivalent: 5×83 + 2×82 + 6×81 + 4×80

= 5×512 + 2×64 + 6×8 + 4×1

= 2560 + 128 + 48 + 4

= 2740

Hence, (5264)8 = (2740)10

Octal digit is represented in 3 bits. An octal number is converted to its binary equivalent by just substituting the respective binary value for each digit of the octal number.

Binary Table

 Octal Binary 0 000 1 001 2 010 3 011 4 100 5 101 6 110 7 111

Convert (3206)8 into Binary

Solution:

Octal Number: 3 2 0 6

Binary Equivalent: 11 010 000 110 (From Binary Table)

Hence, (3206)8 = (11010000110)2

There is no any direct method to convert octal number into octal. So, at first the given octal number is converted into its binary equivalent then the result will be converted into hexadecimal as in previous methods.

Octal Number: 3 2 5 6

Binary Equivalent: 11 010 101 110 (From Binary Table)

Again,

Equivalent (4 bits): 110 1010 1110 (pairing from right-most digit)

Hexadecimal Equivalent: 6 A E (From Binary Table)

Hence, (3256)8 = (6AE)16

0%
• ### The number with base eight is called ______.

hexa decimal number
binary number
decimal number
octal number

56
78
45
55

1133
1324
1345
1323

110101
110111
110100
10101

110111
110011
110101
10101

57B9
34F8
39B6
39F5

16
8
2
10

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