A hub usually has four new ports but can have many more. You plug the hub into your computer and then connect your devices (or other hubs) to the hub. By chaining hubs together, you can create dozens of available USB ports on a single computer.
The USB standard allows devices to receive their power from USB connections. A high-power device like a printer or scanner will have its own power supply, but low-power devices like a mouse and digital camera get their power from the bus to keep them simple. Power (up to 500 milliamps at 5 volts for USB 2.0 and 900 milliamps for USB 3.0) comes from the computer.
If you have a lot of self-powered devices (like printers and scanners), then you don’t need a powered hub; None of the devices connected to the hub need additional power, so the computer can handle it.
If you have a lot of non-powered devices like mice and cameras, you probably need a powered hub. The hub has its own transformer and provides power to the bus so that devices do not overload the computer’s supply.
USB Process
When the host computer turns on, it polls all devices connected to the bus and assigns an address to each one. This process is enumeration; Devices are also numbered when connected to the bus. The host also learns what type of data transfer it wants to perform from each device:
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interrupt: A device that will send very little data, such as a mouse or keyboard, will select interrupt mode.
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Collective: A device such as a printer that receives data in a large packet uses batch transfer mode. The printer takes a block of data (in 64-byte chunks) and verifies it to make sure it is correct.
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Simultaneous: A streaming device (such as a speaker) uses simultaneous mode. Real-time data flows between the device and the host computer and no error correction is performed.
The host can also send commands or query parameters via control packets.
As devices are enumerated, the host keeps track of the total bandwidth requested by all concurrent and interrupt devices. They can consume 90 percent of the available 480 Mbps bandwidth (USB 3.0 increases this speed to 4.8 gigabits per second).
After 90 percent is used, the host denies access to other concurrent or intermittent devices. Control packets and packets for batch transmissions use the remaining bandwidth (at least 10 percent).
Universal Serial Bus divides the available bandwidth into frames and the host controls the frames. Frames contain 1,500 bytes and a new frame starts every millisecond.
During a frame, simultaneous and interrupt devices have a slot, so they are guaranteed the bandwidth they need. Batch and control transfers use the remaining space. The technical links at the end of the article contain lots of details if you want to learn more.
USB Features
Universal Serial Bus has the following features:
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The computer acts as the main computer.
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Up to 127 devices can be connected to the host computer directly or via USB hubs.
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Individual USB cables can extend up to 5 meters; With hubs, devices can be up to 30 meters (six cables’ worth) away from the host computer.
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With USB 2.0, the bus has a maximum data rate of 480 megabits per second (10 times the speed of USB 1.0).
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A USB 2.0 cable has two wires for power (+5 volts and ground) and a twisted pair cable to carry data. The USB 3.0 standard adds four more cables for data transfer. While USB 2.0 can only send data in one direction (downstream or upstream) at a time, USB 3.0 can transmit data in both directions simultaneously.
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In power cables, the computer can supply up to 500 milliamps at 5 volts. A USB 3.0 cable can deliver up to 900 milliamps.
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Low-power devices (like mice) can get their power directly from the bus. High-power devices (such as printers) have their own power supply and draw minimal power from the bus. Hubs may have their own power supplies to power devices connected to the hub.
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USB devices are hot-swappable, meaning you can plug and unplug them from the bus whenever you want. USB 3.0 cable is compatible with USB 2.0 ports; You won’t get the same data transfer speed as a USB 3.0 port, but data and power will still be transferred over the cable.
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Many USB devices can be put to sleep by the host computer when the computer enters power saving mode.
Devices connected to a USB port rely on the cable to carry power and data.
Next Generation USB Technology
USB2.0
The USB version 2.0 standard was released in April 2000 and served as an upgrade to USB 1.1.
USB 2.0 provided additional bandwidth for multimedia and storage applications and has data transmission speeds up to 40 times faster than USB 1.1. To ensure a seamless transition for both consumers and manufacturers, USB 2.0 had full forward and reverse compatibility with original USB devices and works with cables and connectors made for original USB.
Supporting three speed modes (1.5, 12, and 480 megabits per second), USB 2.0 supports low-bandwidth devices such as keyboards and mice, as well as high-bandwidth devices such as high-resolution webcams, scanners, printers, and high-capacity storage systems . .
The deployment of USB 2.0 allowed computer industry leaders to advance the development of computer peripherals to complement existing high-performance computers.
In addition to improving functionality and encouraging innovation, USB 2.0 improves the efficiency of user applications and allows the user to run multiple PC applications or several high-performance peripherals simultaneously.
USB3.0
The USB 3.0 standard became official on November 17, 2008 [source: Everything USB]. USB 3.0 is 10 times faster than USB 2.0 at 4.8 gigabits per second.
It was intended for applications such as transferring high-definition video images or backing up an entire hard drive to an external drive. As hard disk capacity increased, the need for high-speed data transfer method also increased.
USB-C
Introduced as the new standard in 2014, USB-C technology revolutionized connectivity with its versatile and high-performance features. USB-C offers a significant upgrade over USB 3.0, more than doubling the speed of its predecessor, with data transfer speeds of up to 10 gigabits per second.
This advancement supports the growing demand for fast data transfer, making it ideal for tasks such as quickly transferring ultra-high-definition video or large data files.
The reversible design of USB-C cables and the USB-C port simplifies connections and increases user convenience, while its support for a variety of protocols, including power delivery, enables faster charging and greater functionality across a wide range of devices, from smartphones to laptops. beyond.
We updated this article with AI technology, then had it fact-checked and edited by a HowStuffWorks editor.
More information
resources
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Chan, Norman. “Everything You Need to Know About USB 3.0 Plus Photos of the First Attached Cable.” Maximum computer. 18 August 2008. (28 January 2011)http://www.maximumpc.com/article/features/everything_you_need_know_about_usb_30_plus_first_spliced_cable_photos
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Europe. “Harmonization of charging capacity of common charger for mobile phones – frequently asked questions.” 29 June 2009. (31 January 2011) http://europa.eu/rapid/pressReleasesAction.do?reference=MEMO/09/301
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Everything is USB. “SuperSpeed USB 3.0 FAQ.” February 1, 2011. (February 1, 2011) http://www.everythingusb.com/superspeed-usb.html
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Faas, Ryan. “Will Light Peak leave USB 3.0 in the dust?” IT World. 5 November 2010. (31 January 2011) http://www.itworld.com/hardware/126694/will-light-peak-leave-usb-30-dust
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Ganapati, Paul. “Intel’s Light Peak Technology May Kill USB 3.0.” Wired. April 15, 2010. (January 28, 2011) http://www.wired.com/gadgetlab/2010/04/intels-light-peak-technology-could-kill-usb-30/
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Intel. “Extensible Host Controller Interface (xHCI) Specification for USB 3.0.” (January 31, 2011) http://www.intel.com/technology/usb/xhcispec.htm
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Kingsley-Hughes, Adrian. “Is Intel delaying USB 3.0 to give Light Peak an advantage?” ZDNet. June 3, 2010. (January 31, 2011) http://www.zdnet.com/blog/hardware/is-intel-delaying-usb-30-to-give-light-peak-an-advantage/8493
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Knupffer, Nick. “USB 3.0 for the masses – Myth busting.” Intel. June 11, 2008. (January 31, 2011) http://blogs.intel.com/teknoloji/2008/06/usb_30_for_the_masses_dispelli.php
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Lily, Paul. “Intel’s Light Peak Technology Versus USB 3.0.” Tested. April 15, 2010. (January 28, 2011) http://www.tested.com/news/intels-light-peak-technology-vs-usb-30/160/
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Perenson, Melissa J. “USB 3.0 Is Finally Here.” Computer World. January 10, 2010. (January 28, 2011) http://www.pcworld.com/article/186566/usb_30_finally_arrives.html
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Universal serial bus. “USB 3.0 Specification.” (January 28, 2011) http://www.usb.org/developers/docs/
Original article: Understanding USB Types and Flexible USB System
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