Universal Serial Bus

Older USB connectors are being replaced with USB-C (bottom right). Photo: Stéphane Mottin.

Conclusion: If you are considering investing in new computing devices carefully consider ones equipped with USB-C ports. This is the technology of the present and future. USB-A, USB-B, Mini-B and Micro-B connectors are relics of the past. However, devices with them should not be discarded. Cables with two different USB types on each end enable interconnectivity.

The Universal Serial Bus (USB) standard simplifies and improves the interface between a host computer and peripheral devices, with minimal operator action. Its interface is self-configuring. Connectors are standardized, so any peripheral can use any available receptacle. Usually there are no user-adjustable interface settings. The interface is “hot pluggable”, so peripherals can be used without rebooting the host. Small devices can be powered directly from the interface. Protocols for recovery from errors are defined, increasing reliability.

The USB standard specifies cables, connectors and protocols for connection, communication and supplying power to and between computers (Host or A-side) and peripheral devices (B-side). Peripherals include external disk drives, keyboards, mice and printers. However, they are not the only connectors. Screens typically use HDMI and other video connectors, the subject of a later weblog post. Similarly, Ethernet cables are preferred for connecting desktop computers and other devices to computer networks.

Today, most new Android handheld devices aka smart phones use USB-C (type C) connectors for charging and data transfer. Older Android phones have a Micro-B port. Apple iPhones (since iPhone 5) and most iPads use a Lightning connector. While the USB-C and Lightning look very similar, they are not interchangeable.

Fourth-generation MacBook Pro laptops, first released in October 2016, use USB-C for all data ports, and for charging. Windows laptops using USB-C ports for charging include some Acer Aspire, Asus Zenbook, Dell XPS, HP Sprectre and Lenovo ThinkPad models. Many other laptop models use an assortment of chargers, usually incompatible with everything else.

While the European Union has relied on consensus to standardize handheld device connections, this has not worked. While most manufacturers use USB-C connectors, Apple uses a Lightning connector. Now, the EU has said it will legislate compliance that will force all providers of handheld devices, including Apple, to use USB-C connectors. When implemented, this will probably have implications for the entire world.

USB connectors are at the heart of legacy-free computers, a term devised by Microsoft to describe a PC without a lot of the equipment previously found on beige boxes. Much of it large and slow. Most users appreciate this redesign, and especially the fact that a legacy-free PC must be able to boot (start up) from a USB device. The exception is that gamers, because of latency (time delay) issues, want to retain their PS/2 keyboard connectors.

Work on USB began in 1994, with a mandate from seven companies: Compaq, DEC, IBM, Intel, Microsoft, NEC, and Nortel. The goal was to replace a multitude of connectors with a single interface, and to increase data rates to and from external devices. A development team was established by Intel at Folsom, California led by Ajay Bhatt (1957 – ). The first integrated circuits supporting USB were produced by Intel in 1995.

The USB standard is currently maintained by the USB Implementers Forum (USB-IF), with four generations of specifications: USB 1.x (1996), USB 2.0 (2000), USB 3.x (2008, 2013, 2014, 2017) and USB4 (2019).

USB 1.0 ports are no longer relevant. However, efforts have been made to make all interfaces made after that backwards compatible. Thus, USB4 is backwards compatible with everything between USB 3.2 and USB 2.0.

ProtocolsUSB 2.0
USB 3.0
USB 3.1
USB 3.2
Data rate 480 Mbit/s5 Gbit/s10 Gbit/s20 Gbit/s40 Gbit/2
Type AOriginalBlueBlueNoNo
Type BOriginalBlueBlueNoNo
Type CYesYesYesYesYes

USB 1.0 from 1996-01 provided 12 Mbit/s of data transfer. When USB 2.0 was introduced, an unshielded cable version allowed for the attachment of inexpensive peripherals at a data rate of 1.5 Gbit/s.

USB Connectors

There are two versions of USB connectors one on a device and the other that fits into it on a cable. The device or female connector is referred to as a receptacle or port. The cable or male connector is referred to as a plug. Originally, a USB connection was always between a host or hub at the A connector end, and a device or hub’s upstream port at the B connector end. This is why peripherals, such as printers, use Type-B connectors. With handheld devices, the charger is regarded as the A end, while the device is regarded as the B end. Things are no longer so simple.

Port Type-A Type-B Mini Type-B Micro Type-B USB-C
Pins 4 to 9 4 to 9 4 to 9 4 to 9 24
Insertion/ removal cycles 1 500 1 500 5 000 10 000 10 000

The Future: USB4 & USB-C

The future of USB connectivity is the USB4 protocol and the USB-C connector. Yes, both of these could be replaced, and probably will be sometime in the future, but both represent reality now. While every USB-C port looks the same, they do not all provide the same functions. The main functions are data, video and power transfer. It is not possible to tell by looking at the port what is incorporated. If there is no documentation stating otherwise, consumers have to assume that they are simply data ports.

The USB-C connector began its use using the USB 3.1 protocol, which allows data transfers at 10 Gbps, theoretically twice as fast as USB 3.0. The USB 3.1 protocol can also be applied to USB 3.1 Type-A ports. Note: USB-IF has created unnecessary name confusion in that 3.0 connectors are also known as USB 3.1 Gen 1 & USB 3.2 Gen 1 x 1 while USB 3.1 connectors are also known as USB 3.1 Gen 2 & USB 3.2 Gen 2 x 1. The new USB 3.2 port was referred to as USB 3.2 Gen 2 x 2. The x 1 or x 2 refers to the number of lanes.

USB4 incorporates the Thunderbolt 3 protocol into the USB mainstream. The Thunderbolt interface was developed by Intel and Apple. It combines PCI Express and DisplayPort into two serial signals and provides DC power. Thunderbolt 1 and 2 use a Mini DisplayPort connector, whereas Thunderbolt 3 uses the USB-C connector.

USB Cables

Depending on phone, computer and vehicle configuration several different cable types may be required. In Scandinavia, Clas Ohlson stores offer a large selection, as do many specialist stores and online stores.

  • Android devices
    • USB-Micro B to USB-A: Connect older Android phones to older chargers, older computers, and older automobile data ports.
    • USB-C to USB-A: Connect newer Android phones & newer iPhones to older chargers, older computers and older automobile data ports.
    • USB-C to USB-C: Connect newer Android phones to USB-PD (power delivery) chargers, USB PD compatible batteries, some computers (with USB-C ports), 12V car chargers, newer automobile data ports.
  • Apple devices
    • Lightning to USB Type-A: Connect most iOS devices to legacy automobile data ports for CarPlay
    • Lightning to USB Type-C: Connect most iOS devices to current generation macOS devices using USB PD compatible batteries, wall chargers, and 12V car chargers.
  • Other
    • USB Type-A to proprietary cable/magnetic connector charger for Apple Watch or Samsung Galaxy Gear/Android Wear or older Apple Mac equipment.

Additional information on USB-C ports will be presented in the two next weblog posts in this series: 7. Video connectors (2020-02-18) and 8. Power supply/ charging (2020-02-25).

An Aside: PS/2 keyboards

First, a PS2 keyboard is not a PS/2 keyboard. The former refers to Sony’s Play Station 2, launched in 2000. The latter, to ports on IBMs third-generation personal computer, the Personal System/ 2, launched in 1987. It is an ancient and outdated system. Yet, gamers often prefer to use PS/ 2 keyboards (and sometimes even mice) for several reasons. First, PS/2 is analog. Whenever a button is pressed, it sends a command to the computer immediately. This contrast with USB, where the computer polls USB ports, and through them attached devices, at a rate dependent on the frequency of the port. Previously, this was about 125 Hz or so, which could introduce a latency (delay) from 0 to about 8 ms. Polling frequency on modern computers is about 1000 Hz, which reduces this latency to a maximum of 1 ms.

PS/2 keyboards also support N-Key rollover, which allows users to press as many keys as they want, simultaneously. This was not possible with USB keyboards, however many newer USB gaming keyboards support this now.

PS/2 peripherals work immediately without drivers. This is especially useful when diagnosing motherboard and related problems that USB devices cannot detect.

PS/2 devices are not hot-swappable. If a device is plugged into a PS/2 port when a computer is operating, the machine will have to be restarted for the device to function.

Unlike keyboards, USB mice have an adjustable polling rate, allowing them to have polling rates of up to 1000 Hz. Thus, they have had far fewer issues than USB keyboards.

PS/2 hardware is being phased out, and is unavailable on many modern gaming motherboards = a printed circuit board containing the main computer components along with various connectors. Unless that hardware is built into the motherboard, there is no point in using PS/2 equipment, and no point in using a USB adapter to correct any of USB’s deficiencies. At that point it is “game over” for PS/2, and the user might as well use USB peripherals.

One Reply to “Universal Serial Bus”

  1. An article in Gizmodo compares the guidance computers aboard the Apollo 11 spacecraft with a modern USB charger. Forrest Heller analysed the processing power, memory and storage capacity of an 18W Google Pixel charger, a Huawei 40W SuperCharge an Anker PowerPort Atom PD 2 charger as well as the Apollo 11 guidance computer (AGC).

    A direct comparison is difficult. However, the AGC has about 5,600 electronic gates, capable of performing nearly 40,000 simple mathematical calculations every second. This gives it a speed of about 1.024 MHz. The Anker PowerPort Atom PD 2 USB-C charger includes a Cypress CYPD4225 processor running at 48 MHz and twice the RAM and storage capacity. See: https://gizmodo.com/developer-finds-usb-chargers-have-as-much-processing-po-1841598560

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