Probabilistic or deterministic operations on Ising spins or classical bits can perform the unitary time evolution of quantum mechanics, or the unitary gates of quantum computing. Quantum subsystems obtain from classical statistical systems by restriction to a subset of correlation functions. The quantum formalism with the density matrix or wave functions, and non-commutative operators for observables, arises naturally in this setting. We propose a possible realization of Q qubits by 3Q classical bits. We discuss static memory materials based on equilibrium states of generalized Ising models that show interference effects in the bulk, depending on boundary conditions. Neural networks can learn quantum gates. We argue that quantum mechanics can be embedded in classical probabilistic theories, without the need of separate axioms.