e defined by the user to
best fit his source language.

FLOATING POINT SUBROUTINES

A set of subroutines are provided with the PDP-3 to perform floating
point arithmetic. In these, the PDP-3 36 bit word is divided to form a
27 bit mantissa, a, and 9 bit exponent, b. Numbers, thus, appear in the
form: k = ax2^b where, a, is considered to be in fractional form in the
range 1/2 <= a < 1, and b is an integer, 0 <= b < 29. This gives number,
k, the range 10^{-76} < k < 10^{+76}.

The subroutines are called with one operand in the accumulator. After
the subroutine has been executed, the accumulator contains the answer.
Thus floating point numbers are essentially handled as regular logical
works. The format of the number allows magnitude comparisons to be made
by conventional arithmetic as bit 0 is the sign of the number, bits 1 to
9 the exponent, and the remaining 26 bits, together with the sign bit,
the mantissa in ones complement arithmetic. The arithmetic subroutines
are: add, subtract, multiply, divide, convert a floating point number to
binary, convert a binary number to a floating number. Additional
routines form: [square root of x], e^x, ln x, sine(~pi~/2)x,
cos(~pi~/2)x, tan^{-1}x. There are also programs to convert between
floating decimal numbers and PDP-3 floating numbers.

Routines which require two operands, e.g., add, subtract, multiply and
divide, require an index register to specify the address of the second
operand. An index register also specifies parameters in data
conversions, e.g., the position of the binary point when converting a
binary number to a standard floating number.

Using the floating point subroutines, additional routines may be written
which handle complex floating numbers and vector and matrix algebra.

MAINTENANCE ROUTINES

Maintenance Routines are used exclusively to check the operation of the
machine. These routines are operated while varying the bias supply
voltages, and thus a check is made on possible degradation of all
components which would affect the operation of the machine.

MISCELLANEOUS ROUTINES

A variety of additional programs are provided with PDP-3.

One of the more important programs is the Typewriter Interrogator
Program (TIP). TIP allows the typewriter to be used most effectively as
an input-output link by which programs and data are examined and
modified. The features include request for printing of a series of
registers, interrogation and modification