) and is now managed by the USB Implementers Forum (USB-IF), to do one thing: combine all of the peripheral ports into one, both to avoid needing those ports and to standardize how the devices behave. By the mid 2000s, practically all of the older peripheral ports were made obsolete, with only specialty computers still including the serial and parallel ports previously used. The keyboard/mouse PS/2 port is still included on many motherboards, likely due to people using older keyboards such as the legendary IBM Model M keyboard.USB Basics
The basic way the USB protocol works is there's a USB controller that handles communication between the devices and the rest of the system. Multiple controllers can be daisy chained for up to 128 devices, including the controllers. USB ports by default supply up to 2.5W (500mA at 5V) and communicate at a low data rate, which is generally enough for the device to at least talk to the USB controller with information about what it is. From there, the device can request other things like a higher data rate or what kind of power it needs. If all goes well and the device doesn't need a specialized driver or software, the device is good to go and the user can start using the device.On the device side of things, the standard defines, well, standard device profiles which standardizes how the device lets the computer know what it is and how to send data to it. This removes the need for drivers just so the computer can know how to talk to a device. For instance, if you have a mouse that follows the device profile for computer mice, then the computer doesn't need to know the exact mouse you plugged in. The computer just knows there's a mouse that's plugged in and will interpret the data the device is sending as such. This is unlike the early days where a serial port mouse needed a driver to talk to a specific mouse. However, standard device profiles doesn't preclude any fancy things the device can also do, such as RGB lighting or using software to adjust the settings on the device. This does lead to some scary implications with hackers though, as they can plug in a device that pretends to be one thing, but is really another such as with the BadUSB project.
For even more technical bits, the "serial" part in USB means that it uses serial communication. That is, it only sends one bit at a time. It's just capable of shoving a lot of bits in a given amount of time. In addition it also uses what's known as differential signaling, where the signal and its inversion are sent. This is to help with noise (the two signals cancel each other's noise out) and helps detects errors (the other end "adds" the values together and expects a 0).
Connectors
As devices that needed a removable cable became smaller and thinner, namely from the growing PDA and cellphone market, the connectors had a shrinkage. First came the USB mini connector, then eventually the USB micro connector. Both the mini and micro connectors had a Type A and Type B, but most people only encountered the Type B side since computers still used the full-sized Type A port. Another thing that was added to the micro and mini versions was an additional pin to allow the device to act as a USB controller, in case if the person wanted to, for example, connect a printer to the device.
There was just one lingering issue with Type A and Type B, regardless of the size of the connector: it only fit one way. In addition, the port didn't have any way to guide a slightly misaligned plug into it and it wasn't obvious which way to plug it without looking at both the plug and connector. This led to a joke where people needed at least three attempts to insert a plug, even after flipping it one way or the other. This is also despite the USB standard's attempt to say that plugs should have the "USB trident" logo in a way such that it faces up if the plug is horizontal or to the right if it's vertical, which of course, manufacturers would either not do that, or the port was not in the correct orientation anyway.
This led to the creation of USB Type C. Type C was designed to be a palindromic connector, where the functions of the pins are mirrored length-wise. This allows the plug to be inserted into port in either direction and still function normally. In addition, the connector adds a boatload of pins, 24 from 9. While most of the time 12 are used, the USB-IF asked "what if this connector could do more than just USB?" This developed into so-called USB-C Alt Modes, where the connector and cable can be reconfigured into another interface. The two main ones are for carrying HDMI or DisplayPort signals, and depending on the capability of said signal, it may leave out USB functionality, leaving the connector only a video output one or a USB one. Though Thunderbolt may also be used, which allows the connector to carry both data and video.
It's worth mentioning that USB-C defines only a connector, not any of the data protocols that it supports. This continues to cause no end of confusion as people might assume that USB-C does anything. Especially if they came from a device where its manufacturer did make the effort to make its USB-C ports do basically everything (a prominent example of this are Apple's MacBook laptops)
Versions and specifications
USB had multiple revisions over the years, but if there's one thing the USB-IF made sure to do, it's to keep USB backwards and forwards compatible. This means a USB 1.0 device can work on a USB 3.2 controller. Conversely, a USB 3.2 device can work in a USB 1.0 controller, albeit with reduced performance. The revisions updated both the data throughput side and the power delivery side. The latter was important as devices such as portable hard drives required more power than the initial 2.5W, often getting more power by having another plug coming out of the cable that connected to another USB port simply to provide extra power.The major headache with all of this is it's not obvious what features a given USB port can do. While there are some ways to tell, via the logo off to the side of the port or what color the plastic tab that supports the pins in the port are, the only way to tell is by looking at the specification sheet for the device the port's attached to. You can also use an app to further verify the capabilities of the device or port, as some shady manufacturers may tell you it's one version of USB, to even using the right plug for it, but the device is only capable of a lesser version. At the very least, you're guaranteed the USB 2.0 spec.
The following is a table describes the USB version and various attributes about it
| USB Version | Data Rate | Power Output | Connector Type | Connector color |
| 1.x | 1.5 Mbps ("Low speed") 12 Mbps ("Full Speed") | 500mA@5V (2.5W) | A/B/C | Black or white |
| 2.0 | 480 Mbps ("High speed") | 500mA@5V (2.5W) | A/B/C | Black or white |
| 3.0 | 5 Gbps ("SuperSpeed 5 Gbps" or "Gen 1") | 900mA@5V (4.5W) | A/B/C | Blue |
| 3.1 | 10 Gbps ("SuperSpeed 10 Gbps" or "Gen 2") | 900mA@5V (4.5W) | A/B/C | Teal |
| 3.2 | 20 Gbps ("SuperSpeed 20 Gbps" or "Gen 2x2" | 1.5A@5V (7.5W) | C | N/A |
| 4 | 40 Gbps ("USB4 40 Gbps" or "Gen 3x2") 80 Gbps ("USB4 80 Gbps" or "Gen 4") | Up to 3A@5V (15W) | C | N/A |
There's also the USB-PD ("Power Delivery") standard. This is a USB-C only spec. This allows for more power to be delivered over the USB cable via higher voltages, as amperage is the limiting factor. Currently up to 240W is doable, but anything past 100W requires a special "E-marked" cable. USB-PD replaced the earlier attempt at higher power delivery known as "USB Battery Charging" for USB Type-A ports. Eventually the USB-IF said "do whatever, as long as it's safe" with regards to Type-A power delivery, leading to proprietary standards such as Anker's PowerIQ and Qualcomm's Quick Charge.
