What is USB (Universal Serial Bus)?

The USB (Universal Serial Bus) is a port used to connect peripherals to a computer.

What is USB (Universal Serial Bus)?

What is the USB Port on the Computer?

An important feature is that it allows devices to operate at higher speeds, such as, on average, about 12 Mbps, which is 3 or 5 times faster than a parallel port device and 20 to 40 times faster than the serial port.


USB was created by seven companies in 1996: IBM, Intel, NorthernTelecom, Compaq, Microsoft, Digital Equipment Corporation, and NEC.

Initially, there was a serial and parallel interface, but it was necessary to combine all the connectors that make a simpler and higher performance connection.

Thus, USB was created at a speed of 12Mb/s, and as a result of improvements, high-speed USB 2.0 was created with speeds up to 480Mb/s, that is, 40 times faster than connections with USB 1.1 cables.

The USB port can transmit at speeds between 1.5 Mbps and 12 Mbps; The parallel port between 600 Kb/s and 1.5 Mb/s and the serial port can be up to 112 Kb/s.

Features in Data Transfer

USB devices are classified into four types according to their data transfer speed:

   Low Speed (1.0)

It provides transfer rates of up to 1.5 Mbps (192 KB/s) and is mostly used by human interface devices, keyboards, mice, and webcams.

   Full Speed (1.1)

This standard provides a transfer rate of up to 12 Mbps (1.5 MB/s), but measurements are said to be required for independent sources.

This was the fastest version before the USB2.0 specification. These devices divide the bandwidth between them based on a LIFO impedance algorithm.

   High Speed (2.0)

It provides transfer speeds up to 480 Mbps (60 MB/s) but generally up to 125Mbps (16MB/s). It is found in almost 99% of today’s computers.

The USB2.0 cable has four lines, a data pair, a power, and a ground.

   Superspeed (3.0)

It has a transfer speed of up to 4.8 Gbps (600 MB/s). It is ten times faster than the previous 2.0 and, according to estimates, was published by Intel in mid-2009 or perhaps by another Hardware company, based on information collected from the Internet.

USB Types

   USB 1.x

USB1.0, released in 1996, has data rates of 1.5 Mbit/s and 12 Mbit/s. It did not allow extension cords or pass-through monitors due to timing and power limitations.

USB1.1 was released in August 1998 and was the oldest revision that led to what Microsoft called the Old PC.

   USB 2.0

USB2.0, launched in April 2000, has high data transfers of 480 Mbit/s. Changes in this release were made through ECN (Engineering Change Notices).

   USB 3.0

The main characteristic is the transfer rate from 480 Mbps to 4.8 Gbps (600 MB/s) multiplied by 10.

Another feature of this port is that the devices that are plugged in and after a while that are no longer used will immediately switch to low consumption status.

At the same time, the current density increases to 500 to 900 milliamps, which serve to supply a mobile phone or portable audio-visual player in less time.

On the other hand, it increases the speed of data transmission, because instead of working with three lines, it does with five lines. In this way, two lines are used to send, the other is used to receive, and the fifth is responsible for feeding the current. Thus, traffic is bidirectional (Full duplex).

In late 2009, manufacturers such as Asus or Gigabyte introduced motherboards with this new bus revision.

Version 3.0 of this universal connector is 10 times faster than the previous one.

Those with a USB2.0 keyboard or mouse will not experience compatibility issues as they will recognize the system in the next generation, but they will not be able to take advantage of the improved data transfer speed of this bus port.

3.0 also includes the UASP protocol, which provides higher speeds than the BOT (Bulk-Only-Transfer) protocol.

   USB 3.1

USB3.1 was released in July 2013 and it has two variants.

  1. It includes the SuperSpeed ​​mode of USB3.0 and is labeled as USB 3.1 Gen 1.
  2. It offers a new SuperSpeed+ transfer mode labeled USB3.1 Gen 2.

SuperSpeed+ increases the maximum data rate to 10 Gbit / s.

   USB 3.2

USB 3.2 (Gen 2×2) was released in September 2017. This variant includes the SuperSpeed ​​and SuperSpeed+ data modes but reaches data rates of 10 and 20 Gbit (1.25 and 2.5 GB/s) via USB-C.

   USB 4.0

Released on August 29, 2019, by USB Implementers, USB4 is based on the Thunderbolt 3 protocol. It supports data rates of 40 Gbit/s, is compatible with Thunderbolt 3 and backward compatible with USB 3.2 and USB 2.0.

Release Notes

Release Date
Maximum Transfer Rate
11 November 1994
December 1994
13 April 1995
Full Speed (12 Mbit/s)
August 1995
November 1995
15 January 1996
Full Speed (12 Mbit/s)
August 1998
Low Speed (1.5 Mbit/s)
April 2000
High Speed (480 Mbit/s)
November 2008
Superspeed (5 Gbit/s)
July 2013
Superspeed+ (10 Gbit/s)
August 2017
Superspeed+ dual-lane (20 Gbit/s)
August 2019
40 Gbit/s (2-lane)

Connectors and Compatibility

The 1.0, 1.1, and 2.0 specifications define two types of connectors to connect devices to the system: A and B. However, in some connectors, the mechanical layer has changed.

For example, IBM UltraPort is a special connector on top of the LCD of IBM notebook computers. It uses a different mechanical connector while maintaining the characteristics of the signals and protocols.

Other small product manufacturers have also developed small connectivity environments and have created a wide variety of products, some of which are of poor quality.

A USB extension called OTG (USB-On-The-Go) allows a port to function as a server or device; this determines which side of the cable is connected to the device. Even after the cable is connected and the units are communicating, 2 units can change roles under the control of a program.

This feature is specially designed for devices such as PDAs, where the USB connection can be connected to a computer as a device and can be connected to a keyboard or mouse as a server.

USB-On-The-Go also has 2 small connectors, mini-A, and mini-B.

Mass Storage

USB implements connections to storage devices using a set of standards called the mass storage device class.

This was originally designed for optical and magnetic memory but now serves to support a wide variety of devices, especially USB memory.

Wireless USB

Wireless USB (often abbreviated as W-USB or WUSB) is a high-bandwidth wireless radio communication protocol that combines the simplicity of using USB with the versatility of the wireless network.

It uses the Ultra-WideBand platform, developed by the WiMedia Alliance, that can reach 480 Mbps in three-meter intervals and up to 110 transmission speeds in ten-meter intervals, and operates in the frequency range from 3.1 to 10.6.

By using suitable adapters and/or cables, a WUSB device can be converted to a USB device and vice versa.


So far, it was born as a medium high-speed input/output standard that allows devices that require a special card to be connected to achieve full performance, making the product more expensive.

In addition, it provides us with a single connector to solve almost any outside communication problem and can create an authentic peripheral network of up to 127 items.

By connecting a pair of USB connectors that are now standard on all motherboards and in the area covering a single 9-pin serial connector today, by connecting all the devices we have (keyboard, mice, modem, printers, speakers, monitors, scanners, digital cameras, video cameras, plotters), we can save space and money without needing our computer to have a special connector for each of these items.

As you can see, it really is a standard required to make life easier, as it has PNP (Plug and Play) capability and hot connection convenience. In short, you can easily mount connectable and removable peripherals without restarting the computer.

Just like ISA cards tend to disappear, all the above-mentioned connectors will disappear from our computer and also eliminate the need to have corresponding drivers for serial devices, parallel, PS/2 mouse on the motherboard or an expansion card.

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