What are USB-A, USB-B and USB-C?
USB-A, USB-B and USB-C are just shapes. Push every plug into every socket in true-scale 3D, flip a USB-C plug and watch its CC wire move, then see why two identical-looking cables can copy a film in 4 seconds or 2 minutes.
▶ Play with it · Read the 60-second explainer · Watch the 40-second video
- The letter is the shape. USB-A is the flat 12 × 4.5 mm plug on computers and chargers, USB-B the squarish printer plug, Mini-B and Micro-B the small device plugs, and USB-C the rounded 8.3 × 2.5 mm oval. All of them carry power (VBUS), ground and the D+ and D− data pair; USB-C has 24 pins in all.
- Why A and B were different. From 1996, A went into the host (the computer, which gives power) and B into the device, so you could never join two computers or two power supplies. Every plug fitted only one way up.
- USB-C is symmetric. The USB-C socket has 12 contacts on each side of its tongue, the second row a half-turned copy of the first. Turn the plug over and pin A1 meets B1. The cable's CC wire lands on CC1 or CC2, telling the socket which way round it is, and resistors on CC decide who gives power and how much.
- Shape is not speed. Data runs from 12 Mbit/s (USB 1.1) and 480 Mbit/s (USB 2.0) to 5, 10, 20, 40 and 80 Gbit/s. A 4 GB film takes about 2 minutes over USB 2.0 and about 4 seconds at 10 Gbit/s. Power is a separate dial: 2.5 W from an old port to 240 W with USB Power Delivery. The slowest part of the chain, often the cable, wins.
- Wear and extra jobs. USB-A is rated for 1,500 plug-ins, Micro-B and USB-C for 10,000, and the springs that wear are in the cheap plug, not the phone. USB-C's fast pairs can also carry DisplayPort video or Thunderbolt.
- Charge safely. India's CERT-In advises using a wall socket with your own charger, your own cable or a power bank rather than public USB ports. Say no if a phone asks to trust an unknown computer, and buy cables from trusted sellers: a wrong resistor in a cheap cable can overload a port.
| Term | Meaning |
|---|---|
| USB | Universal Serial Bus: the standard plugs, wires and rules for connecting and powering devices, first released in 1996. |
| Host and device | The host (often a computer) runs the connection and usually gives power; the device answers it. |
| VBUS and GND | The power pair in every USB plug: 5 V and ground, or more on USB-C when both ends agree. |
| D+ and D− | The original twisted pair that carries USB 2.0 data in every USB cable. |
| SuperSpeed lanes | Extra wire pairs for fast data, from 5 Gbit/s upward. |
| CC pin | Configuration Channel: on USB-C it finds the plug's orientation, the power roles and the current allowed. |
| E-marker | A chip inside a USB-C cable that reports that it can carry 5 A, its speed and its length. |
| Alternate mode | Using USB-C's fast pins for something other than USB data, such as DisplayPort video. |
| Juice jacking | A feared attack in which a tampered public USB port tries to read or infect a phone while it charges. |
Thirty years from a tangle of PC ports to one reversible plug, written into law.
- 1996 · USB 1.0 (The seven USB promoter companies, USA)
- 1998 · The iMac goes all-USB (Apple, Cupertino, California)
- 2000 · USB 2.0: High Speed (USB promoter group, USA)
- 2007 · Micro-USB (USB Implementers Forum, USA)
- 2008 · USB 3.0: SuperSpeed (USB 3.0 Promoter Group, USA)
- 2014 · USB Type-C (USB 3.0 Promoter Group and USB-IF, USA)
- 2019 · USB4 (USB Promoter Group, USA)
- 2022 · India agrees on USB-C (Government of India inter-ministerial task force; BIS, New Delhi)
The full story, with 27 moments, charts, people and 27 sources: glassbox.how/e/usbclear/history. The data lives in history.json.
Made with the Glassbox studio from this box's storyboard (window.glassbox.director). Free to reuse under CC BY 4.0.
| File | What | Size |
|---|---|---|
glassbox/reel.mp4 |
Reel / Short, with captions and soundtrack | 1080×1920 |
glassbox/video.mp4 |
YouTube video, with captions and soundtrack | 1920×1080 |
glassbox/slide-1…10.jpg |
Instagram carousel | 1080×1350 |
glassbox/thumb.jpg |
YouTube thumbnail | 1280×720 |
glassbox/cover.jpg |
Share card and repo social preview | 1200×630 |
glassbox/history-reel.mp4 |
“History in 10 moments” Reel / Short | 1080×1920 |
glassbox/history-slide-*.jpg |
History carousel | 1080×1350 |
glassbox/post.json |
Post copy and schedule used by the publish kit |
This box has no accounts and no ads, and it ships its own fonts and libraries. When you run it yourself it sends nothing anywhere. On glassbox.how, the site's /bar.js also loads Glassbox's analytics: Google Analytics to count visits (it asks first in the EU, UK and Switzerland, and stays off when your browser sends Global Privacy Control or Do Not Track) and ClickTrust to detect bots.
It remembers a few things in your own browser only, and never sends them anywhere:
| Browser storage key | What it holds |
|---|---|
usbclear.v1 |
Which chapters you have opened, your best quiz scores, and sound on or off. |
Exactly what each one sees is at glassbox.how/privacy.
- Code: MIT. Use it, change it, ship it.
- Explanations, text, images and videos (
glassbox.json,glassbox/): CC BY 4.0. Credit “Glassbox, glassbox.how/e/usbclear”. - Third-party parts keep their own licences: three.js (MIT), Geist, Instrument Serif (SIL OFL 1.1).
- The Glassbox name and logo aren't covered by either licence. See the terms.
Found a mistake? Open an issue. Corrections happen in public.
It's plain HTML, CSS and JavaScript. No build step and no dependencies. Run locally, it contacts no other website.
python3 -m http.server 8000Three.js and the fonts ship in vendor/ and fonts/, so it also works offline.
Then open http://localhost:8000.
| File | What |
|---|---|
index.html, css/app.css |
The page and its styles |
js/app.js, js/stage.js, js/ui.js, js/kit.js |
The shared Glassbox 3D engine: chapters, 3D stage, controls, quiz, video director |
js/chapters/*.js |
One file per chapter: the 3D model, controls, text, key terms, quiz and video scenes |
js/usb.js |
Connector sizes and pins, the plug-socket mating rules, the CC resistor divider, data and power tables, and generic 3D plugs, sockets and devices |
glassbox.json |
Title, question, explainer beats, key terms, browser storage and credits shown on glassbox.how |
reel in each chapter |
The storyboard the Glassbox studio records into short videos |
glassbox/ |
The published video, slides, thumbnail and post copy |
fonts/, vendor/three/ |
Self-hosted Geist and Instrument Serif (SIL OFL 1.1) and three.js (MIT) |