is a specific kind of: computer hardware, hardware | memory device, storage device.

is a broader term that covers: non-volatile storage, nonvolatile storage | fixed storage, read-only memory, read-only storage, ROM | real storage | scratchpad | virtual memory, virtual storage | volatile storage.

has as a part: register.

is a part of: computer, computing device, computing machine, data processor, electronic computer, information processing system.