USB

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.

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 generations of USB specifications: USB 1.x, USB 2.0, USB 3.x and USB4.

USB 1.x
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. 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.

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.

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. 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.

USB4
USB4 specifies the inclusion of Thunderbolt 3 to the USB-C form factor. 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.

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-A
USB Type-A, also known as USB-A, is the ubiquitous USB connector format used in many desktop systems. It was first introduced 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. As of 2019, Apple has retired the USB-A connector from most of its product line, with the exception of the Intel-based Mac mini and Mac Pro.

USB-B
USB Type-B, also known as USB-B, was never introduced in any 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. 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.

USB-C
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. Apple's adoption of USB-C led to memes about the need for adapter dongles for physical compatibility with earlier USB devices. However, the entire Mac product line has adopted this connector since then. The USB-C connector also supports USB4, introduced in 2020 with Apple devices based on the Apple M1 processor.

Articles

 * Does My Apple Device Support USB 3.0? by Tom Nelson at Lifewire (2020-02-17)
 * USB4 development complete, here’s what it means for Mac users by Chance Miller at 9to5Mac (2019-09-03)