The data transfer between main memory and the CPU takes place through two CPU registers.

• MAR :   Memory Address Register
• MDR :   Memory Data Register.

If the MAR is k-bit long, then the total addressable memory location will be 2^k.

If the MDR is n-bit long, then the n bit of data is transferred in one memory cycle.

The transfer of data takes place through memory bus, which consist of address bus and data bus. In the above example, size of data bus is n-bit and size of address bus is k bit.

It also includes control lines like Read, Write and Memory Function Complete (MFC) for coordinating data transfer. In the case of byte addressable computer, another control line to be added to indicate the byte transfer instead of the whole word.