The Memory Buffer is the central switching register. The word coming
from or going to memory is retained in this register. In arithmetic
operations it holds the addend, subtrahend, multiplicand, or divisor.
The left 6 bits of this register communicate with the Instruction
Register. The address portion of the Memory Buffer Register communicates
with the Index Adder, the Memory Address Register, and the Program
Counter. In certain instructions, the address portion of the control
word does not refer to memory but specifies variations of an
instruction, thus, the address portion of the Memory Buffer is connected
to the Control Element.