VAX Floating Point Numbers

Note that some VAX models as purchased may not implement some of the formats shown below.  The bits are normalized such that there is one "hidden" bit to the left of the Most Significant Bit (MSB) of the Fraction.  For instance, that results in 24 bits of Fraction for the F_Floating point shown below.
 
The exponent is "Excess 128"; that is, the binary value of these 8 bits must be subtracted by 128 (decimal) to obtain the actual exponent.

For the 32 bits or 8 bytes shown below, the lowest addressed byte is bits 0-7; the next, bits 8-15; and so on. 

F_floating point numbers have the range of approximately plus or minus 2.9E-39 to plus or minus 1.7E+38, with a precision of approximately seven decimal digits.
 
VAX-11 Floating Point Representations: "F_Floating" Structure (32 bit "longword"):
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Fraction (second part): bit 16 is the least significant Sign Bit Exponent Fraction (first part): bit 6 is the most significant

D_floating point numbers have the range of approximately plus or minus 2.9E-39 to plus or minus 1.7E+38, with a precision of approximately 16 decimal digits.
 
VAX-11 Floating Point Representations: "D_Floating" Structure (64 bit "longword"; first 32 bits):
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Fraction: second part Sign 
Bit		 Exponent Fraction (first part): bit 6 is the most significant

second 32 bits:
63 62 61 60 59 58 57 56 55 54 53 52 51 50 49 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32
Fraction: fourth part: bit 48 is the least significant Fraction: third part

G_floating point numbers have the range of approximately plus or minus 5.6E-309 to plus or minus 0.9E+308, with a precision of approximately 15 decimal digits.  The exponent has a bias of 1024 (not 128).
 
VAX-11 Floating Point Representations: "G_Floating" Structure (64 bit "longword"; first 32 bits):
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Fraction: second part Sign 
Bit		 Exponent Fraction (first part): bit 4 is the most significant

second 32 bits:
63 62 61 60 59 58 57 56 55 54 53 52 51 50 49 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32
Fraction: fourth part: bit 48 is the least significant Fraction: third part

H_floating point numbers have the range of approximately plus or minus 8.4E-4933 to plus or minus 5.9E+4931, with a precision of approximately 33 decimal digits.  The exponent has a bias of 16384 (not 1024).
 
VAX-11 Floating Point Representations: "H_Floating" Structure (64 bit "longword"; first 32 bits):
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Fraction: first part Sign 
Bit		 Exponent

second 32 bits:
63 62 61 60 59 58 57 56 55 54 53 52 51 50 49 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32
Fraction: third part Fraction: second part
third 32 bits:
95 94 93 92 91 90 89 88 87 86 85 84 83 82 81 80 79 78 77 76 75 74 73 72 71 70 69 68 67 66 65 64
Fraction:  fifth part Fraction:  fourth part
fourth 32 bits:
127 126 125 124 123 122 121 120 119 118 117 116 115 114 113 112 111 110 109 108 107 106 105 104 103 102 101 100 99 98 97 96
Fraction:  seventh part; bit 112 is the least significant. Fraction:  sixth part