The memory data register is the register of a computer's control unit that contains the contents of a register to fetch or store from or to the computer storage. In computer architecture, a processor register is a small amount of very fast computer memory used to speed the execution of computer programs by providing quick access to commonly used values—typically, the values being in the midst of a calculation at a given point in time. ... The tower of a personal computer (specifically a Power Mac G5). ... A control unit is the part of a CPU or other device that directs its operation. ... The terms storage ( U.K.) or memory ( U.S.) refer to the parts of a digital computer that retain physical state ( data) for some interval of time, possibly even after electrical power to the computer is turned off. ...

The memory data register is half of a minimal interface between a microprogram and computer storage. The other half is a memory address register. A microprogram is a program consisting of microcode that controls the different parts of a computers central processing unit (CPU). ... The terms storage ( U.K.) or memory ( U.S.) refer to the parts of a digital computer that retain physical state ( data) for some interval of time, possibly even after electrical power to the computer is turned off. ... The memory address register is the register of a computers control unit that contains the address of a register to fetch or store from or to the computer storage. ...

Far more complex memory interfaces exist, but this is the simplest that can work.