USB Wiki

Universal Serial Bus (USB) is an industry-standard interface that defines the cables, connectors, protocols, and power specifications used in communication between computers and peripherals. USB was designed to simplify device connectivity by replacing a variety of legacy ports with a universal connection standard.

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Overview

• Full Name: Universal Serial Bus

• First Introduced: January 1996

• Maintained By: USB-IF (USB Implementers Forum)

• Primary Goals:

  • Simplify connections between computers and external devices

  • Provide plug-and-play support

  • Enable hot-swapping (devices can be plugged/unplugged while running)

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USB Generations and Speeds

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Connector Types

Type-A

• The original flat rectangular connector.

• Still widely used on computers, chargers, and peripherals.

Type-B

• Square-ish, used for printers and some older devices.

Mini-USB

• Smaller variant, used in older cameras and MP3 players.

Micro-USB

• Common in Android devices until USB-C replaced it.

USB-C

• Reversible, compact, and capable of carrying data, power, and video.

• Now the standard for most modern devices including phones, laptops, and docks.

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USB Power Delivery (PD)

USB supports both data and power transfer, which evolved significantly over generations:

• USB 2.0: Up to 2.5W (5V @ 500mA)

• USB 3.0/3.1: Up to 4.5W (5V @ 900mA)

• USB Battery Charging Spec: Up to 7.5W (5V @ 1.5A)

• USB Power Delivery (USB PD):

  • Introduced with USB-C

  • Delivers up to 100W (20V @ 5A)

  • USB PD 3.1 supports up to 240W (48V @ 5A), enabling power delivery for laptops, monitors, and even small appliances.

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Key Features

• Plug and Play: Automatic device recognition and configuration.

• Hot Swapping: Devices can be added or removed without rebooting.

• Device Enumeration: The host system assigns addresses and resources dynamically.

• Host-Device Model: USB requires a host controller (usually a PC or hub); devices are peripherals only.

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USB Host, Hub, and Device Roles

• Host: Initiates communication and manages data transfer (usually a PC or smartphone).

• Hub: Expands one USB port into multiple ports; may be powered or unpowered.

• Device: Receives commands and may send/receive data (mouse, keyboard, camera, storage, etc.).

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Common USB Classes

USB supports a wide variety of device classes, each with standardized drivers:

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USB vs. Thunderbolt vs. Other Interfaces

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USB OTG (On-The-Go)

USB OTG allows devices like smartphones to act as hosts to connect other USB peripherals (e.g., a phone acting as a host to a USB flash drive or keyboard).

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Security Considerations

• USB is vulnerable to attacks like BadUSB, USB-based malware, and power surge damage.

• USB firewalls and USB port management software are used in enterprise environments.

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Future of USB

• USB4 v2.0 enables 80–120 Gbps, targeting applications like AR/VR, external GPUs, and 8K displays.

• Expected to co-evolve with Thunderbolt 5, DP2.1, and PCIe tunneling.

• USB-C is mandated in the EU and other regions for universal charging, pushing industry-wide adoption.

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USB Implementers Forum (USB-IF)

USB is standardized and promoted by the USB-IF, a consortium of companies including Intel, Microsoft, Apple, HP, and others. The USB-IF also handles:

• Specification development

• Logo certification

• Compliance testing

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