OCTAL AND HEXADECIMAL NUMBER CONVERSION

The conversion from and to binary, octal, and hexadecimal representation plays an important part in digital computers. Since 2³ = 8 and 2⁴ = 16, each octal digit corresponds to three binary digits and each hexadecimal digit corresponds to four binary digits.The conversion from binary to octal is easily accomplished by partitioning the binary number into groups of three bits each. The corresponding octal digit is then assigned to each group of bits and the string of digits so obtained gives the octal equivalent of the binary number. Consider, for example, a 16-bit register. Physically, one may think of the

register as composed of 16 binary storage cells, with each cell capable of holding either a 1 or a 0. Suppose that the bit configuration stored in the register is as shown in Fig. 3-2. Since a binary number consists of a string of l's and D's, the 16-bit register can be used to store any binary number from 0 to 2¹⁶ - 1. For the particular example shown, the binary number stored in the register is the equivalent of decimal 44899. Starting from the low-order bit, we partition the register into groups of three bits each (the sixteenth bit remains in a group by itself). Each group of three bits is assigned its octal equivalent and placed on top of the register. The string of octal digits so obtained represents the octal equivalent of the binary number.

Conversion from binary to hexadecimal is similar except that the bits are divided into groups of four. The corresponding hexadecimal digit for each group of four bits is written as shown below the register of Fig. 3-2. The string of hexadecimal digits so obtained represents the hexadecimal equivalent of the binary number. The corresponding octal digit for each group of three bits is easily remembered after studying the first eight entries listed in Table 3-1. The correspondence between a hexadecimal digit and its equivalent 4-bit code can be found in the first 16 entries of Table 3-2.

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