Memories of the past

Most modern computers use semiconductor memory (static or dynamic RAM) for storage of programs and data for the central processing unit (CPU), with magnetic disk or flash storage for programs and data that are not currently in use, and flash storage or optical disks (CDs or DVDs) for removable storage.  Several types of storage have previously been used, but are no longer adequate as storage media.

Some of the types of data storage devices that have been used are

• Wired plugboards (active programs)
• Stepper switches (registers and active programs and data)
• Latching relays (active programs and data)
• Open/closed relays (registers and active programs and data)
• Vacuum tubes -- triodes (American) or valves (British) (registers)
• Punched cards (inactive data and offline programs and data)
• Punched paper tape (active and offline programs and data)
• Acoustic delay lines (active programs and data)
• Williams tubes (registers and active programs and data)
• Magnetic cores (registers and active programs and data)
• Plated wire (active programs and data)
• Magnetic drums (active and inactive programs and data)
• Magnetic cards (inactive and offline data)
• Magnetic tape (offline programs and data)
• 'Floppy' disks (inactive and offline programs and data)
• Fusible links (programmable read-only memory, programs)

And the techniques from some media have been used to develop other media:  hysteresis in ferromagnetic metals is similar to that in ferroelectric materials used in place of dielectrics in ferroelectric random access memory (FRAM), and there is research in using a low-current pulse to read FRAM data non-destructively, as some multi-hole magnetic cores could do and as coincident current addressing of magnetic cores could send half-current pulses and only affect the cores that receive two reinforcing pulses.