Buzz
There is an impressive variety of USB connections now available for consumers. Issarawat Tattong / Getty ImagesWhen compared to older methods of connecting devices to your computer, such as parallel ports, serial ports, and specialized internal cards, Universal Serial Bus connectors are remarkably straightforward.
In this section, we'll explore USB types from both a user-friendly and a technical perspective. You'll discover why the USB system is so adaptable and how it seamlessly supports such a vast range of devices.
Why USB Connectors Are So Convenient
Anyone who has worked with computers for a while knows the problem that Universal Serial Bus solves: In the past, connecting devices to computers was a real challenge.
- Printers were connected to parallel printer ports, with most computers offering just one. External storage devices, which require high-speed connections, often used the parallel port too, though with limited success and speed.
- Modems relied on the serial port, as did some printers and various devices like PDAs and digital cameras. Most computers only had two serial ports, and they were generally slow.
- For faster connections, devices came with their own cards that had to be installed inside the computer’s case. However, card slots were limited, and some cards were tricky to install.
The goal of USB was to eliminate all these issues. The Universal Serial Bus has provided a unified, simple, and efficient method for connecting up to 127 devices to a computer.
Different USB Cable Types
A rectangular socket is the standard USB socket.Connecting a USB device to a computer is straightforward: Locate the USB port on the back of your machine and plug the USB connector into it. (Modern computers and mobile devices are increasingly equipped with USB-C ports.)
When you plug in a new device, the operating system automatically detects it and prompts you for the driver disk. If the device has been previously installed, the computer activates it and establishes communication. USB devices can be connected and disconnected at any time. Below are a few types of USB cables:
USB Type-A
A standard USB connector, referred to as the "A" connectionMany USB devices come with an integrated cable featuring an "A" connection. This widely used type of connector has a flat, rectangular shape and can only be inserted one way.
USB Type-B
A standard "B" connection.USB Type-B connectors are commonly used for larger devices. This connector has a nearly square shape with a slightly beveled top corner, which makes it easier to insert correctly.
Type-B connectors are typically found at the opposite end of a Type-A cable. (The "A" connector faces "upstream" towards the computer, while the "B" connector faces "downstream" to connect with individual devices.)
USB Type-C
A USB-C cable is sleek and reversible, allowing you to plug it in either way. It is ideal for high-speed data transfer and power delivery across various devices.
The USB Type-C connector is compatible with the USB 3.1 standard, supporting data transfer speeds of up to 10 Gbps and power delivery up to 100 watts, enabling faster charging and improved data handling.
USB Mini
A mini-USB, or USB-mini connector, links smaller devices like digital cameras, MP3 players, and older mobile phones to computers for data transfer and charging. It's smaller than the standard USB Type-A connector but larger than newer connectors like Micro-USB and USB Type-C.
Mini-USB comes in two primary versions: Mini-A and Mini-B. While mostly replaced by Micro-USB and USB Type-C in most modern electronics, Mini-USB is still occasionally used.
USB Micro
A USB-micro connector is a more compact version of USB interfaces, primarily designed for small, portable devices like smartphones, tablets, and digital cameras. It comes in two variations: Micro-A and Micro-B.
USB Hubs
Most modern computers come equipped with at least one or two USB ports. But with the large number of USB devices available today, it's easy to run out of ports quickly. For example, you might have a keyboard, mouse, printer, microphone, and webcam all using USB. This leads to the question: "How can you connect all these devices?"
The simple solution is to purchase an affordable USB hub. The USB standard allows up to 127 devices, and USB hubs are part of that standard.
A standard four-port USB hub accommodates four "A" connections.A hub typically has four ports, though some models feature many more. You connect the hub to your computer, then plug your devices (or additional hubs) into it. By linking hubs together, you can expand your USB ports, potentially adding dozens to a single computer.
The USB standard allows devices to draw power through their USB connection. High-power devices such as printers and scanners have their own power supply, but low-power devices like mice and digital cameras receive power directly from the bus, simplifying their design. The power (up to 500 milliamps at 5 volts for USB 2.0 and 900 milliamps for USB 3.0) is provided by the computer.
If you use a lot of self-powered devices (like printers and scanners), a powered hub isn't necessary; none of the devices connected to the hub require extra power, so the computer can provide everything needed.
If you have numerous unpowered devices like mice and cameras, a powered hub is likely necessary. The hub includes its own transformer and provides power to the bus to prevent the computer’s power supply from being overloaded.
The USB Process
When the host system boots up, it communicates with all connected devices, assigning each one a unique address. This procedure is known as enumeration. Devices are also enumerated when they are plugged into the bus. The host then determines the type of data transfer each device requires:
- Interrupt: Devices like a mouse or keyboard, which transmit small amounts of data, opt for interrupt mode.
- Bulk: Devices like printers, which receive large blocks of data, use the bulk transfer mode. The printer receives data in 64-byte packets and verifies its integrity.
- Isochronous: Devices that stream real-time data, such as a speaker, use isochronous mode. Data flows uninterrupted between the device and host without error checking.
The host is also capable of sending commands or querying parameters using control packets.
As devices are enumerated, the host tracks the overall bandwidth usage by isochronous and interrupt devices. These devices can collectively use up to 90% of the available 480 Mbps bandwidth (USB 3.0 increases this rate to 4.8 Gbps).
Once 90 percent of the bandwidth has been consumed, the host will prevent any additional access from isochronous or interrupt devices. Any leftover bandwidth, at least 10 percent, is utilized by control packets and those used for bulk transfers.
The Universal Serial Bus allocates the available bandwidth into distinct frames, with the host managing the assignment of these frames. Each frame holds 1,500 bytes, and a new frame initiates every millisecond.
During each frame, isochronous and interrupt devices are granted a specific slot to ensure they receive the necessary bandwidth. Bulk and control transfers take advantage of any remaining space. For additional details, refer to the technical links provided at the end of the article.
USB Features
Inside a USB cable, there are two power wires — +5 volts (red) and ground (brown) — alongside a twisted pair of data-carrying wires (yellow and blue). The entire cable is shielded for protection.The Universal Serial Bus is equipped with several key features, including:
- The computer serves as the host.
- Up to 127 devices can be connected to the host, either directly or through USB hubs.
- USB cables can extend up to 5 meters in length; with the use of hubs, devices can be located as far as 30 meters (equivalent to six cables away) from the host.
- USB 2.0 offers a maximum data transfer rate of 480 megabits per second, which is ten times faster than USB 1.0.
- A USB 2.0 cable includes two power wires (+5 volts and ground) and a twisted pair of wires for data transmission. USB 3.0 introduces four additional wires to enhance data transmission. Unlike USB 2.0, which transmits data in one direction at a time, USB 3.0 supports simultaneous two-way data flow.
- The computer can supply up to 500 milliamps of power at 5 volts through the power wires. In contrast, USB 3.0 cables can provide up to 900 milliamps of power.
- Low-power devices, such as mice, draw power directly from the bus. High-power devices, like printers, rely on their own power supplies and only take minimal power from the bus. Hubs can also have their own power supplies to support connected devices.
- USB devices are hot-swappable, meaning you can plug and unplug them at any time. While a USB 3.0 cable will work with a USB 2.0 port, it won't achieve the same data transfer speed but will still support power and data transfer.
- When the host computer enters a power-saving mode, many USB devices can be put into sleep mode by the host.
Devices connected to a USB port rely on the cable to transmit both power and data.
Subsequent Generations of USB Technology
USB 2.0
The USB 2.0 standard was released in April 2000, offering an improvement over USB 1.1.
USB 2.0 provided increased bandwidth to accommodate multimedia and storage needs, achieving data transfer speeds 40 times faster than USB 1.1. It was designed to be fully compatible with both older USB devices and the cables/connectors made for them, ensuring a seamless transition for consumers and manufacturers.
With three speed options (1.5, 12, and 480 megabits per second), USB 2.0 supports both low-bandwidth devices like keyboards and mice, and high-bandwidth devices such as high-definition webcams, scanners, printers, and large-capacity storage systems.
The introduction of USB 2.0 enabled leaders in the PC industry to further innovate and develop new peripherals that complemented the growing capabilities of high-performance computers.
USB 2.0 not only boosted functionality and fostered innovation but also enhanced user productivity, allowing for the simultaneous use of multiple applications or several high-performance peripherals.
USB 3.0
The USB 3.0 standard was officially introduced on November 17, 2008 [source: Everything USB]. This version of USB offers data transfer speeds that are 10 times faster than USB 2.0, reaching 4.8 gigabits per second.
Designed with applications like transferring high-definition video or backing up entire hard drives in mind, USB 3.0 was developed as the demand for higher-speed data transfer methods grew alongside increasing hard drive capacities.
USB-C
USB-C, launched in 2014, brought a major leap forward in connectivity technology, offering enhanced versatility and performance. It provides data transfer speeds of up to 10 gigabits per second, more than double the speed of USB 3.0.
This development meets the increasing need for fast data transfer, making it perfect for tasks such as quickly moving ultra-high-definition video or large data files.
The USB-C cable's reversible design and the USB-C port make connections easier and more user-friendly. In addition, its compatibility with various protocols, including power delivery, allows for faster charging and enhanced functionality across a wide range of devices, from smartphones to laptops and more.
