SGPIO is an acronym for Serial General Purpose Input/Output which is a 4-signal (or 4-wire) bus used between a host bus adapter (HBA) and a backplane

Backplane

A backplane is a group of connectors connected in parallel with each other, so that each pin of each connector is linked to the same relative pin of all the other connectors forming a computer bus. It is used as a backbone to connect several printed circuit boards together to make up a complete...

; of the 4 signals, 3 are driven by the HBA and 1 by the backplane. Typically, the HBA is a storage controller located inside a server, desktop, rack or workstation computer which interfaces with hard disk drives (HDDs) to store and retrieve data.

The SGPIO specification has the official name SFF-8485 and is maintained by the SFF Committee

Small Form Factor committee

The Small Form Factor committee is an ad hoc electronics industry group formed to quickly develop interoperability specifications ....

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