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Introduced in January 1996, USB was designed to replace traditional serial and parallel ports with a single, user-friendly interface. Today’s ecosystem consists of five connector types: Type-A, Type-B, Type-C, Mini-USB, and Micro-USB. Each serves a different host or peripheral role; Mini-USB was phased out in May 2007, and Micro-USB was standardized in January 2007.
The USB standard has evolved from 12 Mbps (USB 1.1) to 480 Mbps (USB 2.0), and has entered the gigabit arena with USB 3.x and USB4. Core benefits such as plug-and-play simplicity, support for up to 127 devices from a single host, and a standardized plug-and-jack design have remained constant throughout the generations.
Robust cable test specifications – 90 Ω ± 15 % differential impedance, 30 Ω ± 30 % standard mode impedance, ≤ 26 ns/m delay, and ≤ 100 ps offset – ensure signal integrity for a wide range of applications, from simple charging to high-speed data and video.
USB Connector Types
Type-A
The rectangular Type-A plug connects to host computers (PCs, game consoles, and hubs) to provide power and data to peripherals, such as flash drives, keyboards, and mice. USB 2.0 Type-A uses four pins; USB 3.x adds five pins for transferring superfast data at up to 5 Gbps.
Type-B
The Type B plug is square with a beveled top corner, allowing for the connection of downstream devices such as printers, scanners, and some external hard drives. The larger form factor enhances mechanical stability and enables repeated plugging and unplugging.
Type-C
Introduced in August 2014, USB-C is a reversible 24-pin connector measuring approximately 8.3 mm × 2.5 mm in size. It supports ultra-high-speed data (up to 20 Gbps in USB 3.2 Gen 2×2), alternate-mode video (DisplayPort/HDMI), and power transfer of up to 100 W (using a 5 A, 20 V cable). As the physical basis for USB4, it can transfer at rates of up to 40 Gbps, and up to 80 Gbps according to the unofficial “version 2.0”.
Mini-USB
Mini-USB (Mini-A/B/AB) was standardized with USB 2.0 in 2000 and was commonly found in early digital cameras. In May 2007, the USB-IF deprecated the Mini-A/AB variant, and the use of Mini-B declined in favor of smaller formats.
Micro-USB
The micro-USB (Micro-A/B/AB) standard was introduced in January 2007 for devices that are thinner than those using mini-USB. It can power smartphones, tablets, and mobile power supplies at speeds of up to 480 Mbps. Although Micro-USB is still used in budget and legacy devices, it is being gradually replaced by USB-C.
USB Standards Evolution
| Standard | Marketing Name | Max Speed | Introduced |
|---|---|---|---|
| USB 1.1 | Full-Speed USB | 12 Mbps | Aug 1998 |
| USB 2.0 | Hi-Speed USB | 480 Mbps | Apr 2000 |
| USB 3.2 Gen 1 | SuperSpeed USB | 5 Gbps | Nov 2008 |
| USB 3.2 Gen 2 | SuperSpeed+ USB | 10 Gbps | Jul 2013 |
| USB 3.2 Gen 2×2 | SuperSpeed+ Dual | 20 Gbps | 2017 |
| USB4 | USB4 | 40 Gbps | 2019 |
| USB4 2.0 | USB4 Version 2.0 | 80 Gbps | 2022 |
Key Advantages of USB
- Plug & Play: Plug and play with built-in drivers automatically recognized by modern operating systems.
- Multi-Device Support: A single host controller can address up to 127 devices through the hub.
- Standardized Design: Unified connectors and signals reduce cable clutter and user confusion.
- Cost-Effective: Centralized host intelligence reduces peripheral complexity and manufacturing costs.
USB Cable Test Specifications
| No. | Parameter | Test Method | Requirement |
|---|---|---|---|
| 1 | Differential Impedance | TDR | 90 Ω ± 15 % |
| 2 | Common Mode Impedance | TDR | 30 Ω ± 30 % |
| 3 | Propagation Delay | TDR | ≤ 26 ns/m (≈ 5.2 ns/ft) |
| 4 | Skew | TDR | ≤ 100 ps per cable |
| 5 | Attenuation | S-parameter (S21) measurement | ≤ 3.2 dB @ 200 MHz; ≤ 5.8 dB @ 400 MHz |
Frequently Asked Questions
Q1: Which connector handles the most power?
USB-C with Power Delivery supports up to 100 W (20 V × 5 A) of bi-directional power flow and is the preferred choice for laptops and high-power docks.
Q2: Why was Mini-USB deprecated?
USB-IF phased out Mini-A/AB in May 2007 and replaced it with the smaller, more ruggedized Micro-USB introduced in January 2007.
Q3: How many USB devices can I cascade?
With a cascading hub, a single USB host controller can support up to 127 devices, excluding the root hub.
Conclusion
From its inception in 1996 to the present day, the Gigabit USB4 era, USB has been the cornerstone of modern wired connectivity. By choosing the right connector, whether it’s the classic Type-A for legacy hosts or the versatile USB-C for power and video, and adhering to cable testing standards, you can ensure a reliable, high-performance connection between all your devices. Keep this guide handy to choose the best USB solution for any situation.
Are you looking to explore USB cables more? Check out these related posts:
- What is a Micro USB Cable?
- Is USB Tethering Faster Than Ethernet?
- Custom USB Cable Assemblies
- What is a USB to TTL Serial Cable?
- What is the Best Fiber Optic USB?
Apple Liu, Romtronic’s Marketing Manager, specializes in driving Asian market growth. With a degree in International English and eight years of sales experience in the electronic cable and harness industry, she brings deep industry expertise and a global perspective. She is passionate about Romtronic’s leadership in digital engineering and is dedicated to advancing the brand’s presence and innovation.
