# USB Standard-B plug > a class of legacy USB plugs (peripheral device end) that preceded USB-C **Wikidata**: [Q133871408](https://www.wikidata.org/wiki/Q133871408) **Source**: https://4ort.xyz/entity/usb-standard-b-plug ## Summary The USB Standard-B plug is a class of legacy USB connectors located at the peripheral device end of a cable. It served as the standard interface for connecting devices before the adoption of the USB-C standard. ## Key Facts * **Definition:** A class of legacy USB plugs designed for the peripheral device end of a connection. * **Succession:** This connector class preceded the introduction of the reversible USB-C plug. * **Classification:** It is a subclass of the USB Standard-B connector, the USB Standard plug, and the USB Type-B plug. * **Topology:** The "B" designation indicates the peripheral device end, distinguishing it from Type-A plugs, which serve as the host end in pre-C USB architectures. * **Variations:** The class includes specific iterations such as the USB 2 Standard-B plug and the USB 3 Standard-B plug. * **Distinction:** It is structurally different from the USB Standard-B receptacle (the port on the device) as well as USB Micro-B and USB Mini-B plugs. * **Official Recognition:** The designation "USB Standard-B plug" is officially recognized in USB-IF documentation, including the USB 3.1 Legacy Cable and Connector specification. ## FAQs ### Q: What is the primary function of the USB Standard-B plug? A: The USB Standard-B plug is designed to connect to the peripheral device end of a USB cable (the "B" side), as opposed to the host or computer end (the "A" side). ### Q: Is the USB Standard-B plug still the current standard? A: No, it is considered a class of legacy plugs. It represents the connectors used prior to the widespread adoption of the USB-C standard. ### Q: How does the USB Standard-B plug differ from Standard-A? A: In pre-C USB connections, the "B" indicates the peripheral device end, while "Type-A" refers to the host or computer connection end. ## Why It Matters The USB Standard-B plug represents a foundational era in the connectivity landscape, defining how peripheral devices interacted with hosts for decades. Before the unification brought by USB-C, the distinction between "A" (host) and "B" (peripheral) plugs was essential to the Universal Serial Bus architecture, enforcing a strict directional flow of data and power. This class of connectors facilitated the adoption of standardized peripherals, ensuring that devices like printers and hard drives had a universal, distinct interface that prevented improper cabling loops. The existence of this specific "Standard-B" class (separate from the smaller Mini and Micro variations) highlights the evolution of robust, full-sized connectors required for stable, high-bandwidth data transfer in stationary or larger devices. As the industry has transitioned to the reversible USB-C, the Standard-B plug serves as a historical marker of the specific, directional topologies that governed early USB implementations. ## Notable For * **Defining Peripheral Connectivity:** It specifically denotes the peripheral device end in the legacy USB hierarchy. * **Pre-C Architecture:** It is the primary connector class that existed before the USB-C standard unified host and peripheral connections. * **Structural Rigidity:** Unlike the smaller Mini and Micro variants, the Standard-B plug class represents the full-sized, non-portable-optimized connector block. * **Version Iterations:** The form factor accommodated technological evolution, notably encompassing distinct physical designs for USB 2.0 and USB 3.0 speeds. ## Body ### Definition and Classification The USB Standard-B plug is formally classified as a legacy USB plug situated at the peripheral device end of a cable. In the hierarchy of USB connectors, it acts as a subclass for the USB Standard-B connector, the broader USB Standard plug category, and the USB Type-B plug family. ### Historical Context This class of plugs is defined by its position as the precursor to modern USB-C technology. In the pre-C era, USB connections were strictly directional, requiring different physical connectors for the host (Type-A) and the device (Type-B). The Standard-B plug was the "upstream" connector designed to attach to external devices. ### Variations and Differentiation The USB Standard-B plug class encompasses specific hardware iterations, most notably the **USB 2 Standard-B plug** and the **USB 3 Standard-B plug**. While both serve the peripheral end, they represent different generations of the standard. It is distinct from several related entities: * **USB Standard-B Receptacle:** The plug is the male connector on the cable, whereas the receptacle is the female port on the device. * **USB Standard-A plug:** The counterpart connector that plugs into the host computer. * **Micro and Mini Variants:** The Standard-B plug is the full-sized version, distinct from the smaller USB Micro-B and USB Mini-B plugs designed for mobile devices. ### Official Documentation The terminology and specifications for this plug are documented in key technical references, including the *USB 3.1 Legacy Cable and Connector Revision 1.0*, the *USB Type-C Cable and Connector Specification*, and the *USB 3.2 Revision 1.1* (June 2022). ## References 1. [Source](https://www.usb.org/document-library/usb-31-legacy-cable-and-connector-revision-10) 2. [Source](https://www.usb.org/document-library/usb-type-cr-cable-and-connector-specification-release-24) 3. [Source](https://www.usb.org/document-library/usb-32-revision-11-june-2022) 4. [Source](https://www.usb.org/document-library/usb-type-cr-connectors-and-cable-assemblies-compliance-document-rev-21b) 5. [Source](https://www.usb.org/document-library/universal-serial-bus-31-legacy-connectors-and-cable-assemblies-compliance-document)