USB Port - History, Design and General Features

It has become one of the most important ports today, and everything connects through this connector. The USB port has become a vital standard for all types of users and no one sees a computer without a large number of these ports. The Universal Serial BUS (USB) has had many attempts to be replaced, but to no avail.

In this article, we are going to review the history of this connector and take a look at the features of the most modern versions. This type of connector has been developed for communication and power supply between a computer and peripherals. The first connector version was in 1996 and since then The USB Implementer Forum (USB-IF) is responsible for maintaining it and its standard

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USB port history

The start of development was in 1994 and was led by Compaq, DEC, IBM, Intel, Microsoft, NEC and Nortel. The aim was to develop a simple connector for peripherals that will replace the existing clumsy and complex connectors. It also sought to address the usability issues of the time and to simplify software configuration as much as possible. Additionally it was sought to offer higher data speeds for external devices.

Ajay Bhatt and his team worked on the development of this standard at Intel, and the first integrated circuits were created by Intel in 1995. The USB 1.0 standard was introduced in January 1996 with a low speed data transmission of 1.5Mbit / s. and 12Mbit / s at full speed.

Early designs required a single speed 5Mbit / s bus. Low speed is added to support low cost peripherals with unshielded cables. The 12Mbit / s speed was especially intended for high-speed devices, such as printers or floppy drives. The low speed of 1.5Mbit / s was developed for transferring data from peripherals such as keyboards, mice, and joysticks.

Microsoft Windows 95 OSR 2.1 was the first operating system to support this connector in August 1997. The first fully commercial version was called USB 1.1 and was released in September 1998.

The first device to offer this type of connectivity was the Apple iMac, which with its great success, made this port popular. Apple's decision to remove all legacy ports from iMac, manufacturers without legacy PC developer. This quickly became standardized.

Temporal evolution USB port

The USB Implementers Forum (USB-IF) ratified the 2001 standard launched in April 2.0 in 2000. Those in charge of developing this standard were: Hewlett-Packard, Intel, Lucent Technologies (now Nokia), NEC and Philips. Work was done to offer a great jump in data transfer speed, going from 12Mbit / s of USB 1.1 to 480Mbit / s of version 2.0. We are talking about a speed improvement of x40 times.

This 2.0 standard was replaced on November 12, 2008 by the 3.0 standard. Data transfer was drastically improved, reaching up to 5Gbit / s, consumption was reduced, output power was increased, and backward compatibility with version 2.0 was offered. The 3.0 standard integrates a higher speed bus, called SuperSpeed ​​in parallel with the 2.0 standard. The first computers to integrate this standard were launched in January 2010.

It is estimated that in 2008 there were more than 6.000 billion ports and interfaces of this type on the market worldwide. It is estimated that each year 2.000 billion USB ports and interfaces were added.

In December 2014 the USB-IF published the specifications of the USB 3.1 port, USB Power Delivery 2.0 and the Type-C connector. They are included within the international standard IEC 62680 (Universal Serial Bus Interfaces for Data and Power). The specifications for USB 3.2 were released in September 2017.

USB-IF published the specifications of the USB4 standard on August 29, 2019. 

USB standard lens

The USB interface was sought to simplify and improve the connectors of personal computers and peripherals. Previously the interfaces were either very crude or were solutions of each manufacturer. The universal serial bus facilitates usability in the following ways:

• It is self-configuring, eliminating the need for the user to adjust parameters such as speed or data format. Also suppresses settings such as interrupts, I / O addresses, or direct memory access channels
• The USB connector is standardized for the host
• USB takes full advantage of the potential of peripherals to manage themselves. Devices with this standard often do not have user adjustment interface
• Hot swappable
• Small devices can be powered directly through this interface, eliminating the need for additional cables
• This certificate is only obtained after testing compliance with the standard. Provides the user with confidence that devices based on this standard will function properly without problems
• Common error recovery protocols are defined, improving reliability
• Installing a USB device requires a very small number of actions on the part of the operator. When we connect a device based on this standard, it is automatically configured using the existing device driver

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Benefits for hardware and / or software developers

Above all, it offers advantages in the simplicity of its implementation:

• USB standard eliminates the need to develop proprietary interfaces for new peripherals
• Supports a large number of transfer speeds, adapting to keyboards, mice or any other peripheral
• USB allows you to adapt the design to obtain the best possible latency for critical functions or we can configure it for background transfers of massive data with a low impact on system resources
• Universal Serial Bus interface generalizes without signal lines dedicated to a single function of a device

Limitations of the USB standard

Despite its benefits, the universal serial bus has certain limitations regarding its design:

• Cables are limited in length because the standard is limited to nearby peripherals. This means that it moves in the area of ​​the work table, not supporting communication between rooms or buildings. Such a port, however, can be connected to a gateway to access distant devices.
• It has a strict tree network topology and master / slave protocol for peripheral connection. It prevents devices from interacting with each other, requiring a host, and it also does not allow two hosts to communicate through these types of ports. There is an extension to this limitation via USB On-The-Go
• Host can send signals to all peripherals based on this standard simultaneously, but must address them individually. Very high speed peripheral devices require sustained speeds not available in this standard.
• There are converters between legacy interfaces and this standard, they may not offer a complete implementation with legacy hardware. For example, a USB to parallel converter can handle a printer fine, but not with a scanner that requires bi-directional use of the data pins.

For device developers, this standard requires implementing a complex protocol and a 'smart' driver within the device. The developers of these devices for sale to the general public require obtaining a USB ID. This implies that they must pay a fee to the IF-USB and sign an agreement with this organization. In addition, using the logo of this standard requires annual dues and memberships in the body.

Previous versions of the standard

We review the versions of the standard prior to the official launch:

• November 1994 - USB 0.7
• December 1994 - USB 0.8
• April 1995 - USB 0.9
• August 1995 - USB 0.99
• November 1995 - USB 1.0 Relase Candidate

USB 1.x standard

The first version of the USB 1.0 standard was released in January 1996 and had two types of speeds. The low speed offered a data transfer speed of 1.5Mbit / s and a maximum speed of 12Mbit / s. This standard does not allow extension cables or step monitoring, due to time and power limitations.

This first version of this standard was hardly adopted, it was with version 1.1, released in August 1998, when it began to be adopted. This version was the first to have wide adoption and Microsoft designated it as "PC without legacy".

Both versions of this type of connector were limited to the Type-A and the Type-B, the latter a compact version of the Type-A. It should be noted that many designs appeared for a miniaturized Type-B connector integrated into many peripherals. This caused the lack of uniformity in the USB 1.x standard and hindered the treatment of peripherals. A more compact version of the Type-A connector was not developed until USB 2.0 rev 1.01.

USB 2.0 standard

This standard was launched in April 2020 and now offers a speed rate of 480Mbit / s (60MB / s). This speed standard was referred to as 'high speed' or 'high bandwidth'. Modifications to the specifications of this connector have been made through Engineering Change Notices (ECN). The most important modifications are:

• Mini-A and Mini-B connector
• Micro USB Cables and Connectors Specification 1.01
• USB InterChip Supplement
• On-The-Go USB 1.3 plug-in that enables two devices with this connector to communicate with each other without the need for a separate host
• Battery Charging Specifications 1.1: Added support for dedicated chargers, sharing host chargers for devices with depleted batteries
• 1.2 Battery Charging Specifications: With a current of 1.5A at the card ports for unconfigured devices, allowing high-speed communication while offering a current of 1.5A and a maximum current of 5A
• Link Power Management ECN Addendum Adding a Sleep Power State

USB 3.x standard

The specifications for this standard was officially released on November 12, 2008, developed by USB-IF. Its official announcement was on November 17, 2008 during the SuperSpeed ​​USB Developers Conference.

This first version would offer a SuperSpeed ​​transfer, being compatible with plugs and cables of previous versions. All SuperSpeed ​​devices are identified by the logo and connectors, which have turned blue.

SuperSpeed ​​offers a nominal transfer rate of 5.0Gbit / s, and is also compatible with all three supported transfer modes. Efficiency depends on several factors, including encoding of physical symbols and link-level overhead. Under 5Gbit / s signaling speeds with 8b / 10 encoding, each byte needs 10bits for transmission, so throughput without processing is 500MB / s. Considering aspects such as flow control, packet framing and protocol overhead, it drops to 400MB / s (3.2Gbit / s)

Low power and high power devices can work equally under this standard. Those devices based on SuperSpeed ​​allow to take advantage of the increase in current between 150-900mA.

This standard offers support for the UASP protocol, which offers generally faster transfer speeds than the Bulk-Only-Transfer protocol.

USB 3.1 version

This two-variant version was released in July 2013. The Gen1 retains the SuperSpeed ​​transfer mode and the Gen2 introduces a new version of this SuperSpeed ​​+ transfer mode. The SuperSpeed ​​+ version offers double the maximum data signal speed, going to 10Gbit / s. At the same time, this variant offers a reduction in overhead on line encoding by just 3% by moving to a 128b / 132b encoding scheme.

USB 3.2 version

This is the latest version and was introduced in September 2017. It retains the SuperSpeed ​​and SuperSpeed ​​+ data transfer modes, but two new transfer modes are added for SuperSpeed ​​+ via the USB Type-C connector offering data speeds of 1.25GB / s and 2.5GB / s. The increased bandwidth is the result of the operation of several existing lanes that were designed for the flip-flop capabilities of the Type-C connector.

Naming scheme

USB4 standard

The specification was released on September 29. This standard is based on the specifications of the Thunderbolt 3 protocol, offering a data transfer speed of 40Gbit / s. This architecture establishes a method to share a single high-speed link for various types of end devices in a dynamic way, seeking the best data transfer according to type and application.

During CES 2020, both USB-IF and Intel highlighted that they would allow USB4 to support all of the Thunderbolt 4 options. The first products to support this standard are expected to be the Intel Tiger Lake and AMD Zen3, which would arrive in late 2020. .