Quantum Random Access Machine (QRAM), is a virtual hardware model for computation and may prove to be better suited for the interpretation of quantum programming languages. The QRAM models allows unitary transformations and measurements to be freely interleaved via a quantum device controlled by a classical computer.
The quantum device would contains a large, but finite number of individually addressable quantum bits, much like a classical RAM memory chip contains a multitude of bits.
The classical control computer sends a sequence of instructions, which are either of the form "apply" unitary transformation U to qubits i and j or "measure" qubit i. The quantum device carries out these instruction, and responds by making the results of the measurements available.