Here is a full 32-bit register. Each box labelled "bit" contains the single bit circuit of the previous page.

As the instruction word and copy start signal from the executor flow down the bus, each register's "register control logic" or "RCL" "sees" those bits.

Each RCL has a unique 8-bit register number encoded in it (detailed on the next page). The purpose of the RCL is to detect its own address as the source or destination for the current instruction and signal either EN-OUT or EN-IN accordingly, thereby causing the register's data bits to flow out to the bus, or in from the bus.

And thus, as the copy start and instruction word from the Executor flow down the bus, some one register, the source of the instruction, reacts and puts its data onto the bus, and some one register, the destination of the instruction, reacts and receives its data from the bus -- and thus a copy between them is effected.