OCTAL CODE

The octal numeral system, or oct for short, is the base-8 number system, and uses the digits 0 to 7. Numerals can be made from binary numerals by grouping consecutive digits into groups of three (starting from the right). For example, the binary representation for decimal 74 is 1001010, which groups into 001 001 010 — so the octal representation is 112.

In decimal systems each decimal place is a base of 10. For example:

In octal numerals each place is a power with base 8. For example:

By performing the calculation above in the familiar decimal system we see why 112 in octal is equal to 64+8+2 = 74 in decimal.

Octal is sometimes used in computing instead of hexadecimal.

THIS IS AN 8-BIT CODE HENCE HERE THE NUMBERS FROM 0-7 CAN BE REPRESENTED

0=0000
1=0001
2=0010
3=0011
4=0100
5=0101
6=0110
7-0111

Usage

In computers

Octal is sometimes used in computing instead of hexadecimal, perhaps most often in modern times in conjunction with file permissions under Unix systems (see chmod). It has the advantage of not requiring any extra symbols as digits (the hexadecimal system is base-16 and therefore needs six additional symbols beyond 0–9). It is also used for digital displays.

At the time when octal originally became widely used in computing, systems such as the IBM mainframes employed 24-bit (or 36-bit) words. Octal was an ideal abbreviation of binary for these machines because eight (or twelve) digits could concisely display an entire machine word (each octal digit covering three binary digits). It also cut costs by allowing Nixie tubes, seven-segment displays, and calculators to be used for the operator consoles; where binary displays were too complex to use, decimal displays needed complex hardware to convert radixes, and hexadecimal displays needed to display letters.

All modern computing platforms, however, use 16-, 32-, or 64-bit words, with eight bits making up a byte. On such systems three octal digits would be required, with the most significant octal digit inelegantly representing only two binary digits (and in a series the same octal digit would represent one binary digit from the next byte). Hence hexadecimal is more commonly used in programming languages today, since a hexadecimal digit covers four binary digits and all modern computing platforms have machine words that are evenly divisible by four.

The prefix customarily used to represent an octal number is "o" (i.e. o73), as binary and hexadecimal are represented by 'b' and 'h' respectively.

Conversion between bases

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Decimal – Octal Conversion

Method of consecutive divisions by 8

Is used to convert integer decimals to octals and consists in dividing the original number by the largest possible factor of 8 and successively dividing the remainders by successively smaller factors of 8 until the factor is 0. The octal number is formed by the quotients, written in the order of its obtention. for example convert the following to octal 75.8 solution:- 125/8^2=1 125-((8^2)*1)=61 61/8^1=7 61-((8^1)*7)=5 125(base10)=175(base8)

900/8^3=1

900-((8^3)*1)=388

388/8^2=6

388-((8^2)*6)=4

4/8^1=0

4-((8^1)*0)=4

4/8^0=4

900(base10)=1604(base8)

Method of consecutive multiplications by 8

Is used to convert a decimal fraction to octal. The decimal fraction is multiplied by 8, and the integer part of the result is the first digit of the octal fraction. The process is repeated with the fractionary part of the result, until it is null or within acceptable error parameter. Example: Convert 0.140625 to octal: 0.140625 x 8 = 1.125

0.125 x 8 = 1.0

Previous methods can be combined to convert decimal numbers with integer and fractionary parts.

If you want to convert decimal number to other number system as hexadecimal, octal, binary etc. You must divide the number by the number system you converting to. For example decimal to hexadecimal:610

3050/16 = 190 rem 10 190/16 = 11 rem 14 11/16 = 0 rem 11 asw: BEA

remember when you write your answer you start from bottom to the top.

Octal – Decimal Conversion

Use the formula:

Example: Convert octal 764 to decimal system. 764 (base 8) = 7 x 8² + 6 x 8¹ + 4 x 8° = 448 + 48 + 4 = 500 (base 10)

For double digit numbers this method amounts to taking the first number, multiplying it by 8 and then adding the second to get the total. Example: 65 in octal would be 53 in decimal (6*8 + 5 = 53)

Octal – Binary Conversion

To convert octals to binaries, replace each digit of octal number by its binary correspondent. Example: Convert octal 1572 to binary.

1 5 7 2 = 001 101 111 010

Binary – Octal Conversion

The process is the reverse of previous algorithm. The binary digits are grouped 3 by 3, from the decimal point to the left and to the right. Then each trio is substituted by the equivalent octal digit.

For instance, conversion of binary 1010111100 to octal:

001	010	111	100
1	2	7	4

Thus 1010111100₂ = 1274₈

Octal – Hexadecimal Conversion

The conversion is made in two steps using binary as an auxiliary base. Octal is converted to binary and then to hexadecimal, grouping digits 4 by 4, which correspond each to an hexadecimal digit.

For instance, convert octal 1057 to hexadecimal:

To binary:

1	0	5	7
001	000	101	111

To hexadecimal:

0010	0010	1111
2	2	F

Thus 1057₈ = 22F₁₆