Parallel ATA
Micron Technology's Hybrid Memory Cube (HMC) stacked memory uses a serial interface. Many other computer buses have migrated towards replacing parallel buses with serial buses, for example by the evolution of Serial ATA replacing Parallel ATA, PCI Express replacing PCI, and serial ports replacing parallel ports. In general, serial buses are easier to scale up and have fewer wires/traces, making circuit boards using them easier to design.