nd
is left with the remainder.

The logical functions AND, inclusive OR, and exclusive OR, are formed in
the Accumulator.

Carry Storage Register

The Carry Storage Register facilitates high-speed multiply and is
properly part of the Accumulator.

In-Out Register

The In-Out Register is the main path of communication with external
equipment. It is also part of the Arithmetic Element. In multiplication
it ends with the low order digits of the product. In division it starts
with the low order parts of the dividend and ends with the quotient.

The In-Out Register has a full set of shifting properties, (arithmetic
and logical).

* * * * *

There are three registers of 15 bit length which deal exclusively with
addresses. The design allows for expansion to 18 bits. These registers
are:

Memory Addressing

The Memory Address Register holds the number of the memory location that
is currently being interrogated. It receives this number from the
Program Counter, the Index Adder or the Memory Buffer.

Program Counter

The Program Counter holds the memory location of the next instruction to
be executed.

Index Adder

The Index Adder is a 15 bit ring accumulator. The sum of an instruction
base address, Y, and the contents of an index register, C(x), are formed
in this register. This register holds the previous content of the
Program Counter in the "jump and save Program Counter," jps,
instruction. The Index Adder also serves as the step counter in shift,
multiply, and divide.

* * * * *

The Control Element contains two six bit registers and several
miscellaneous flip-flops. The latter deal with indexing, indirect
addressing, memory control, etc. The six bit registers are:

Instruction Register

The Instruction Register receives the first six bits of the Memory
Buffer Register during the cycle which obtains the instruction from
memory (cycle zero). This information is the primary input to the
Control Element.

Program Flags

The six Program Flags act as convenient program switches. They are used
to indicate separate states of a program. The program can set, clear, or
sense the individual flip-flops. The program can also sense or make the
state "All Flags ZERO." They can also be used to synchronize various
input devices which occur at random times (see Input-Output, Typewriter
Input).

* * * * *

Three toggle