Storage

Storage interfaces are where embedded designs quietly lose their performance. The flash device is fast, the controller is fast, and the measured throughput is a third of the figure on the datasheet. The gap is almost always in the interface: command queuing, transfer mode, alignment, or a power state the driver never leaves.

Three families, three sets of constraints

Serial ATA comes from the PC world and brought native command queuing with it. Its strength is mature tooling and predictable behaviour on rotating and solid-state media alike; its cost is a protocol stack heavier than most embedded systems need.

UFS was designed for mobile: full duplex, command queuing, low power states that matter as much as peak bandwidth. It is where high-end embedded storage has converged, and its power management is the part that most often surprises.

SD UHS-II keeps the removable card format and adds a differential interface underneath it. The compatibility rules between UHS-I and UHS-II hosts and cards are the part that produces the most support tickets.

What the courses cover

Serial ATA III (IS3), Universal Flash Storage UFS 2.0 (IS4) and SD UHS-II (IS5) each work from the specification down to the signalling, with the protocol traces that show where the throughput actually goes.