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Universal Serial Bus
Certified USB.svg
Released:USB 0.7: November 11, 1994
USB 1.0: January 15, 1996
Developer:Compaq, DEC, IBM, Intel, Microsoft, NEC, and Nortel
Vendor:USB Implementers Forum (USB-IF)
Operating system:USB 1.1: Mac OS 8.1 or later
USB 2.0: Mac OS X 10.2.7 or later
USB 3.x: Mac OS X 10.7.3 or later
USB-C  : OS X 10.10.2 or later
USB4    : macOS Big Sur (11) or later

Universal Serial Bus (USB) is an industry standard that establishes specifications for cables and connectors and protocols for connection, communication and power supply (interfacing) between computers and peripherals.[1]


Intel Rock Star Ajay Bhatt

The USB specification was co-created at Intel by Ajay Bhatt in collaboration with Compaq, DEC, IBM, Microsoft, NEC, and Nortel. First released as USB 1.0 in January 1996, the USB standards are currently maintained by the USB Implementers Forum (USB-IF). There have been four major generations of USB specifications: USB 1.x, USB 2.0, USB 3.x and USB4.[2]

Version history

Name Released Maximum transfer rate Note
 USB 0.7 1994-11-11 ? Pre-release
 USB 0.8 1994-12 ? Pre-release
 USB 0.9 1995-04-13 Full Speed (12 Mbit/s) Pre-release
 USB 0.99 1995-08 ? Pre-release
 USB 1.0-RC  1995-11 ? Release Candidate
 USB 1.0 1996-01-15 Low Speed (1.5 Mbit/s)
Full Speed (12 Mbit/s)
 USB 1.1 1998-08
 USB 2.0 2000-04 High Speed (480 Mbit/s)
 USB 3.0 2008-11 Superspeed (5 Gbit/s) Also referred to as USB 3.1 Gen 1[3] and USB 3.2 Gen 1 × 1
 USB 3.1 2013-07 Superspeed+ (10 Gbit/s) Includes new USB 3.1 Gen 2,[3] also named USB 3.2 Gen 2 × 1 in later specifications
 USB 3.2 2017-08 Superspeed+ dual‑lane (20 Gbit/s) Includes new Gen 1 × 2 and Gen 2 × 2 multi-lane modes[4]
 USB4 2019-08 Dual‑lane (40 Gbit/s) Includes new Gen 3 × 1 and Gen 3 × 2 modes and introduces USB4 routing for tunnelling of USB3.x, DisplayPort 1.4a and PCI Express traffic and host-to-host transfers, based on the Thunderbolt 3 protocol

USB 1.x

USB symbol.jpg

USB 1.1 was introduced with the iMac G3 in 1998. At the time, it was considered a shock to the classic Mac OS user base because it replaced several legacy connectors, such as ADB, GeoPort, and SCSI. However, Apple Computer's adoption of the standard drove the rest of the PC industry to quickly embrace it.[5] Support was built into Mac OS 8.1 and later, but third party PCI cards required a USB Card Support extension. Support for USB drives required a USB Storage Support extension.

A USB 2.0 to 30-pin connector for early iPods and iPhones.

USB 2.0

USB 2.0 was introduced with the updated Aluminum PowerBook G4, new Power Mac G5, and 3rd generation iPod in 2003. Support was built into Mac OS X 10.2.7 "Jaguar" and later. The Classic environment can recognize USB 2.0 drives through Mac OS X, but booting in Mac OS 9 itself will fall back to USB 1.1 speeds.[6]

USB 3.x

USB 3.0 was introduced with the updated MacBook Air and MacBook Pro in mid-2012. Support was built into Mac OS X 10.7.3 "Lion" and later. The first iOS device to support USB 3 through its Lightning port was the iPad Pro in 2015.[7] Unlike PC manufacturers which label their USB 3 ports blue, Apple does not designate their computer ports by color. Access to the System Information application can identify the port type.[8]


USB4 specifies the inclusion of Thunderbolt 3 to the USB-C form factor.[9] It was introduced by Apple in November 2020 in new MacBook Air, 13-inch MacBook Pro, and Mac mini models based around the Apple M1 processor.[10]

Form factors

USB connectors came in many formats to accommodate desktop, portable, and mobile equipment. This is distinct from USB version and some connector types were modified to add support for newer versions of USB. Most have been deprecated from future usage (with the exception of USB-C) to reduce confusion in new devices.


USB Type-A, also known as USB-A, is the ubiquitous USB connector format used in many desktop systems. It was first introduced by Apple Computer in the iMac G3 with support for USB version 1.1. The same connector could be used with Apple devices that supported USB 2, starting in 2003. With the introduction of support for USB 3 in Apple devices in 2012, the connector was modified with 5 additional pins to increase throughput. USB-A cables and ports with USB 3 support look externally similar to older versions, and were often identified with a blue color or "Superspeed" logo. However, Apple has never identified their USB port versions in this manner. Subsets of the USB-A connector have also been introduced for smaller devices, such as Mini-A and Micro-A, though none of these were ever adopted by Apple.[11] As of 2021, Apple has retired the USB-A connector from most of its product line, with the exception of the Mac mini, Intel-based iMac, and Mac Pro.[12]


USB Type-B, also known as USB-B, was never designed into any standalone Apple device, but was adopted by many peripherals such as printers and scanners. Subsets of the USB-B connector were introduced for smaller devices, such as Mini-B and Micro-B. Since 2011, Apple has included USB Micro-B adapters with iPhones (which use proprietary connectors) to comply with European Union regulations. A USB Micro-B port was also included on 2nd and 3rd-generation Apple TV models for use by authorized service providers only. Support for USB 3 forced the USB-B and Micro-B connectors to be enlarged to accommodate additional pins. As a result, newer "Superspeed" USB-B cables can only be used on USB 3 devices; older USB-B cables are backwards compatible and can also be used on USB 3 devices, but at slower USB 2 speeds.[11][13][14]


USB Type-C, also known as USB-C, was introduced with the MacBook with Retina Display in 2015. Support was built into OS X 10.10.2 "Yosemite". The connector type is also used for Thunderbolt 3, but can also be used for USB 3.x signals without Thunderbolt, causing confusion among some users.[15] Apple's adoption of USB-C led to memes about the need for adapter dongles for physical compatibility with earlier USB devices.[16][17] However, the entire Mac product line has adopted this connector since then.[12] The USB-C connector also supports USB4, introduced in 2020 with Apple devices based on the Apple M1 processor.[10]

Power delivery

USB is specified to deliver power at various levels. This has become a common method of charging mobile devices. Standard USB 1.x and 2.0 ports can output up to 500 mA at 5 volts (2.5 watts) while USB 3.1 can output up to 3 amps.[18] USB-C ports can output up to 5 amps at 20 volts (100 watts).[11]


Though standard USB devices are supposed to negotiate power output levels, rogue devices known as "USB Killers" are known to exploit this by using capacitors to absorb delivered power and then return it in 110 or 220 volt bursts until the host device or USB controller is destroyed. Some versions are commercially sold for the purpose of electrical "testing".[19][20] However, graduate student Vishwanath Akuthota was jailed and fined for damaging or destroying over US$50,000 in computer equipment (including iMacs) at the College of Saint Rose with such a USB Killer stick.[21]


  1. "USB deserves more support", Simson, 1995-12-31. Retrieved on 2011-12-12. 
  2. Hachman, Mark (2019-03-04). The new USB4 spec promises a lot: Thunderbolt 3 support, 40Gbps bandwidth, and less confusion (en).
  3. 3.0 3.1 USB 3.1 Specification- Language Usage Guidelines from USB-IF. Archived from the original on 12 March 2016.
  4. Peter Bright (2017-07-26). USB 3.2 will make your cables twice as fast… once you’ve bought new devices. Archived from the original on 2017-07-27. Retrieved on 2017-07-27.
  5. #1 Temporal Loop - Birth of the iMac by Thomas Hormby, The Mac Observer. 2007-05-25. Archived 2007-05-29.
  6. USB 2.0 in macos9 by supernova777, Mac OS 9 Lives. 2014-09-15.
  7. iPad Pro 12.9 Teardown.
  8. Does my Computer have USB 2.0 or USB 3.0 Ports? by Josh, Tether Talk. 2014-10-21.
  9. USB4 Specification Announced: Adopting Thunderbolt 3 Protocol for 40 Gbps USB by Anton Shilov, AnandTech. 2019-03-04.
  10. 10.0 10.1 Apple unleashes M1, Apple Inc. 2020-11-10.
  11. 11.0 11.1 11.2 USB-A vs. USB-C: What’s the difference? by Tyler Lacoma, Digital Trends. 2020-11-20.
  12. 12.0 12.1 Mac mini vs. Mac Pro: The affordable alternative by Anthony Casella, iMore. 2019-06-22.
  13. Apple releases Micro USB adapter for iPhone by Dieter Bohn, The Verge. 2011-10-04.
  14. Identify your Apple TV model, Apple Inc. 2019-03-25.
  15. About the Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter, Apple Inc. 2019-12-11.
  16. No Jack City... by Joshua Fruhlinger and Andrew Thompson, Ceros Originals. 2018-08-24.
  17. Apple, the company once mocked dongles, is in love with them now by Selene Kyle, The TechNews, Medium. 2016-11-07.
  18. What are the Maximum Power Output and Data Transfer Rates for the USB Standards?, Cadence PCB Solutions. 2020-06-08.
  19. The USB Killer, version 2.0 by Brian Benchoff, Hackaday. 2015-10-10.
  20. USB Killer now lets you fry most Lightning and USB-C devices for $55 by Sebastian Anthony, Ars Technica. 2017-02-17.
  21. Idiot admits destroying scores of college PCs using USB Killer gizmo, filming himself doing it by Kieren McCarthy, The Register. 2019-04-18.

See also

External links