A Load/Store Disjoint instruction, when executed by a CPU, accesses operands from two disjoint memory locations and sets condition code indicators to indicate whether or not the two operands appeared to be accessed atomically by means of block-concurrent interlocked fetch with no intervening stores to the operands from other CPUs. In a Load Pair Disjoint form of the instruction, the accesses are loads and the disjoint data is stored in general registers.