The Serial ATA (SATA) interface has been the primary way to connnect drives to computers for many years, but despite a few upgraded iterations, it's hit a roadblock on goosing faster speeds from devices like solid-state storage, where higher throughputs is one of the key selling points.
That ground had been ceded to the PCI Express (PCIe) interface, so perhaps it should come as no surprise that SATA proponents decided to take advantage of the faster PCIe standard to create the SATA Express interface. It uses connectors that can make use of PCIe lanes to effectively increase the bandwidth up to nearly 2GBps for SATA drives and double data transfer speeds to 12Gbps. (It's still compatible with legacy SATA devices.)
Asus appears to be the first manufacturer to embrace SATA Express, recently sending around prototypes of its Hyper Express drive enclosures to sites like Legit Reviews and The Tech Report. The enclosure can house a pair of drives in a 3.5-inch case -- either for 2.5-inch drives or mSATA or m.2 SSDs. Supposedly when it becomes available in the U.S., Hyper Express will ship without drives. Any drives used in Hyper Express are configured in a RAID 0 configuration, which helps to maximize performance.
The prototypes shipped with twin Kingston 120GB mSATA solid-state drives. According to Legit Reviews, Asus claims that sequential read speeds should approach 745Mbps and write speeds reach 809Mbps. Though the sites' preliminary benchmarking didn't match those speeds, the company has time to tweak its drivers to boost performance.
Hyper Express is expected to reach the market in the next couple of months, and SATA Express will receive a further boost due to Intel supporting the standard in its forthcoming 9-series chipsets (Z97, H97, and X99). Not coincidentally, Asus has just announced new motherboards built around those chipsets, of course including SATA Express support.