Load and store operations in computer systems are extended to provide for Stream Load and Store and Masked Load and Store. In Stream operations a CPU executes a Stream instruction that indicates by appropriate arguments a first address in memory or a first register in a register file from whence to begin reading data entities, and a first address or register from whence to begin storing the entities, and a number of entities to be read and written. In Masked Load and Masked Store operations stored masks are used to indicate patterns relative to first addresses and registers for loading and storing. Bit-string vector methods are taught for masks.