USB-A and USB-B are physically incompatible with each other — they serve opposite ends of a USB connection. USB-A plugs into host devices like computers, while USB-B plugs into peripherals like printers. A standard USB-A to USB-B cable bridges them.
- USB-A end connects to the host (computer, hub)
- USB-B end connects to the peripheral (printer, scanner)
- Both ends share a compatible USB version (2.0, 3.0)
- You try to plug USB-B directly into a USB-C port without an adapter
- You force either connector in the wrong orientation
- You try to connect two USB-A or two USB-B ports directly together
What makes them physically different?
USB-A has a flat, wide rectangular shape. It only inserts one way. USB-B is taller and squarer with beveled top corners — you’ll recognize it from the chunky end of a printer cable. Neither connector is reversible, so forcing them in the wrong way damages the port.
Despite looking different, both connectors carry the same signals. The shape difference is intentional — it prevents you from plugging the wrong end into the wrong device.
USB-A vs USB-B: side-by-side comparison
| Aspect | USB Type A | USB Type B |
|---|---|---|
| Shape | Flat, rectangular | Square with beveled corners |
| Used on | Computers, hubs, chargers | Printers, scanners, external drives |
| Durability | ~1,500 cycles | ~5,000 cycles |
| Reversible | No | No |
| Common versions | USB 2.0, 3.0, 3.1 | USB 2.0, 3.0 |
Which cable do you need?
For most printers and older external drives, a standard USB-A to USB-B cable is all you need. Make sure both device ports support the same USB generation — a USB 3.0 cable works in a 2.0 port but only at 2.0 speeds. According to the USB Implementers Forum, USB standards are designed to be backward compatible, so newer cables generally work with older hardware at reduced speeds.
If your computer only has USB-C ports, you’ll need a USB-C to USB-B adapter or cable. A standard USB-B plug will not fit a USB-C port directly. If you’re exploring what USB-C can do, see whether USB-C can connect to HDMI for more on USB-C capabilities.
Common setups at a glance
| Setup | Works? | Need | Note |
|---|---|---|---|
| PC USB-A to printer USB-B | Yes | USB-A to USB-B cable | Most common setup |
| USB-C laptop to printer USB-B | Yes | USB-C to USB-B cable | Requires correct cable |
| USB-B to USB-B direct | No | — | Not a valid connection |
| USB-A to USB-A direct | No | — | Host-to-host not supported |
If you’re also dealing with display connections from a USB-C device, check whether USB-C supports video output before buying adapters.
Bottom line: USB-A and USB-B are designed to work together, not interchangeably. USB-A goes in the host; USB-B goes in the peripheral. Use a standard USB-A to USB-B cable for printers and scanners, or a USB-C to USB-B cable if your computer lacks USB-A ports. Never force either connector — they only insert one way.