The Evolution of USB Standards from 1.0 to USB 4

Digital Forensic Glossary Jay Ravtole todayJanuary 23, 2024

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The name USB stands for Universal Serial Bus. A “bus” is a circuit link that transfers data or power between components in an electronic system. A “serial” bus sends data one bit at a time via a single wire. USB is an engineering standard that specifies the connectors and cables used to connect various devices in an electronic system.

In short, the USB standard enables simple interconnectivity and data exchange between devices. But it has developed to do much more. The USB protocol and its associated products were developed in response to the challenges of connection complexity and slow data transfer inherent in early 1990s computer systems. The introduction of the USB standard in 1996 simplified and streamlined the patchwork interconnection process. Since then, USB has been a series of speed bumps.

The USB protocol and the products that use it have been refined over the last 25 years, and they continue to evolve. The USB Implementers Forum (USB-IF), a group of over 700 firms that guides the standard, has continually aimed to boost data communication speed as well as power supply. The result has been a greater acceptance of computer technology in the business and computing markets due to quicker device setup and replacement.

Here are some of the specific advancements in the USB standard and associated devices over the years since its initial release. To avoid confusion, we will initially refer to the original naming standard prior to the USB-IF’s modifications in 2013. Throughout this post, we will discuss these developments and the confusion that surrounds them.

The Interconnect Landscape Pre-1996

Prior to the development of USB, computer makers utilized serial and parallel ports, proprietary plugs, connectors, and cables to transfer data, which frequently required dedicated drivers and cards. Data transmission speeds were slow, ranging from 100 kilobytes (kB) per second for parallel to 450 kilobits (kb) per second for serial, and connecting peripherals frequently required disconnecting or restarting the host computer.

The USB-IF initiated the development of the USB standard in 1994. Several versions of the standard (USB 0.8 and USB 0.9) were announced that year as “pre-releases” but were not commercially available. A further pre-release (USB 0.99) was announced in 1995, but it was not publicly available.

USB 1.0

USB 1.0, the USB line’s first major version, was released in early 1996. It supported data transfer rates of 1.5 megabits per second (Mbps) at low speed and 12 Mbps at full speed. It was also self-configuring, which eliminated the need for users to adjust device settings to accommodate accessories. The interface was also hot-swappable, allowing devices to be replaced without restarting the host computer. Despite being the first commercial version of USB, it was not generally adopted by the market, and only a few products were offered to customers.

USB 1.1

The first standard was amended and released in 1998. It was labelled USB 1.1 and had the same data transfer rates as version 1.0, but it could also function at slower speeds for lower bandwidth devices. It was branded as Full Speed. Apple’s iMac G3 adopted the new USB standard and eliminated the use of serial and parallel connections in its devices. This decision paved the path for industry-wide adoption of the USB protocol, as well as widespread consumer adoption of USB products. Versions 1.0 and 1.1 required the use of standard Type A (rectangular) or Type B connectors (square with bevelled top corners).

USB 2.0

As the market acceptance of PCs and their many peripherals grew, and applications became more complicated, the necessity for faster data transfer became clear. USB 2.0 was released in April 2000 and has a data transfer rate of 480 Mbps. However, bus restrictions lowered this to 280 Mbps. It was marketed under the name High Speed. The new version might also function at 12 and 1.5 Mbps for devices that need less bandwidth. It also provided plug-and-play functionality for entertainment and storage devices, as well as support for power supplies via USB ports up to 5 V and 500mA.

Furthermore, it enabled two devices to communicate without the requirement for a separate USB host, a feature known as USB On-the-Go. USB 2.0 supports USB Type A, B, and C connectors, as well as USB Mini and Micro A & B connectors. Micro A and B connections were not released until 2007.

The first commercially available USB flash drives with up to 8 megabytes of storage capacity were produced in 2000, substantially increasing the USB standard’s adoption. Flash drives now have terabytes of storage.

Wireless USB

The wireless USB standard (W-USB) was announced in May of 2005 for wireless short-range network communication with a 10-meter range limit and a speed of 480 Mbps. This standard is no longer in use.

USB Micro

USB micro connections made their debut in 2007. They were essentially smaller versions of USB micro-B connectors that allowed for faster charging and data transfer than microdevices. USB Micro connectors were widely adopted for usage in standardizing connections in Android mobile devices. It should also be noted that USB Micro connectors are a physical standard, not a communication standard like USB 1.0, 1.1, or 2.0.

USB 3.0 (now USB 3.2 Gen 1)

The USB standard’s third major update recognized the market’s continued demand for expanded digital storage and bandwidth. The USB 3.0 specification was released in November 2008. It supported data transfer rates of up to 5 gigabits per second (Gbps), but commonly operated at around 3 Gbps. As a result of this functionality, the standard became known as SuperSpeedUSB. USB 3.0 increased the number of connection lines from four to eight, allowing for bidirectional data transfer. It still supports USB 2.0. Since its launch, USB 3.0 has been updated with 3.2 naming guidelines and is now officially known as USB 3.2 Gen 1.

The USB 3.0 specification also boosted power transmission capacity to 5 V and 900 mA. It is compatible with physical USB 3.0 Type A and B connectors as well as USB Type C. To distinguish the connectors used with 3.0, elements of the devices are colored blue.

USB 3.1 (or USB 3.2 Gen 2×1)

The USB 3.1 version was an interim standard similar to 3.0, although it enhanced data transfer rates to 10 Gbps (USB 3.1 Gen 2). USB 3.1, like USB 3.0, has had its nomenclature updated and is now known as USB 3.2 Gen 2. The improved transfer speeds earned it the name SuperSpeed+. Version 3.1, which was released in July 2013, used the same ports as 3.0 (USB A, B, Mini, and Micro).

In 2014, USB Type C connectors were announced. The Type C connector, introduced in 2012, transmits data, display, and power signals via a single, tiny connector that is also reversible. The Type C connector is oval-shaped and somewhat thicker than the USB Mini and Micro variants, making it roughly one-third the size of the original USB Type A connector. It included more wires and pins, increasing its data capability.

USB 3.2 and USB Type C

USB 3.2 replaced the USB 3.0/USB 3.1 specifications and made some retroactive changes to them. With the continued need for increased speed as a driving component, USB version 3.2, another interim step, was launched in September 2017 and essentially doubled the data transmission speed to 20 Gbps (USB 3.2 Gen 2×2) by increasing the number of data transfer channels from one to two. This was accomplished by installing USB Type C connectors. The boost to 20 Gbps is only achievable with USB Type C cables, which can send 10 Gbps in each direction via two wire pairs.

USB 4.0

USB 4.0, introduced in August 2019, is based on the Thunderbolt 3 standard. It supports data transmission rates of up to 40 Gbps and power transfer rates of up to 240 W, as per the more modern Power Delivery 3.1 standard. Thunderbolt 3 is a technology established by Intel in 2015 to facilitate high-speed data and video transfers.

The USB 4.0 version does not require new connectors and retains the existing Type C connectors. This allows data and video signals to effectively share lanes and maximize the device’s bandwidth use, resulting in faster data transfers. It is also backwards compatible (via adapters) with USB versions 2.0 and 3.2, albeit speeds may be reduced.

This latest version of the USB standard now includes Intelligent Power Delivery, which allows a USB 4.0 cable to transmit as much power as a connected device requires, up to 240 Watts and 5 A. Power delivery is also bidirectional, which means it can flow to and from the connected device.

A Word About Connectors

  • USB Type A: the first, and most widely-known USB connector has been in use since the standard was first released. It has a flat, rectangular shape and is only insertable in one orientation.
  • USB Type B: smaller than Type A and is square in shape with slightly bevelled corners on the top and a large space on the inside.
  • USB Mini-B: compact-sized, 5-pin connector used in older cell phones and digital cameras, largely replaced by the Micro-B.
  • USB Micro-B: smaller and flatter than the Mini-B, used in many smartphones.
  • USB 3.0 Type A: flat and rectangular similar to Type A, but with square pins and blue internals for identification. Also known as SuperSpeed.
  • USB 3.0 Type B: designed for SuperSpeed applications, with two stacked rectangular sections and blue internals for identification.
  • USB 3.0 Micro-B: small, flat and rectangular with two distinct sections. Designed to carry data and power for SuperSpeed applications.
  • USB Type C: reversible symmetrical design with rectangular shape and rounded corners. Newest USB connector device.

The USB standard helped to simplify the maze of connectors and cables that were previously utilized to connect peripheral devices to host computers. The continued growth of this standard and the devices that implement it have resulted in faster data transfer and power delivery via a compact, low-cost, and user-friendly interface.

What started as a way to link peripherals evolved into a tool to improve the user experience for a wide range of products, including smartphones and other mobile devices, games, toys, smart home products, and industrial networking. USB devices are also widely used today for charging purposes.

All of these features helped to create USB the most widely used signal transfer technology in the world today, and the uses for USB technology will only rise. CUI Devices provides a variety of USB connectors and cables in various form factors that are designed to meet several USB standards.

Written by: Jay Ravtole

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