Quick Answer / Summary: A USB A to B cable connects a host computer’s Type-A port to a Type-B device port – the standard link for printers, scanners, and some external drives. It comes in USB 2.0 (480 Mbps) and USB 3.0 (5 Gbps, blue B connector) versions. It is a host-to-device cable, not a data-transfer cable between two computers – connecting two PCs with an A to B or A to A cable can damage the ports.
The USB A to B cable is the connection between a computer’s standard USB port and the squarish port on a printer, scanner, or external drive. It is one of the highest-volume searches in USB cable queries, and the confusion behind it is constant: what is the B end, why does the printer box ship one, and can the same cable move files between two computers. This guide explains the A and B connectors, the USB 2.0 and USB 3.0 versions of the cable, the devices that take the B port, and the one thing an A to B cable must never be used for.
The A End and the B End
The A end is the flat rectangular USB Type-A plug – the port on every computer, hub, and charger. The B end is the smaller squarish connector with two 45-degree beveled corners, the port found on printers, scanners, and some external drives. The cable is asymmetric by design: the A end carries power and data from the host, and the B end delivers them to the device. That asymmetry is the reason the cable is a host-to-device link and never a peer-to-peer link – neither end is a host, and there is no charge pump or transfer logic in the cable to arbitrate between two hosts.
Why the B Port Is Squarish
The Type-B connector’s shape – a square with two cut corners – is a mechanical keying that makes the plug fit only one way and only into a B port. It cannot seat in a Type-A port, which is part of how the standard keeps the host and device roles from being mixed up by accident.
USB 2.0 vs USB 3.0 A to B
The cable exists in two versions. The USB 2.0 A to B is the classic printer cable – four data and power pins, a 480 Mbps ceiling, and the B connector in black or white. The USB 3.0 A to B adds five pins to both connectors for the SuperSpeed pairs – the A end is the blue-tongued 9-pin Type-A, and the B end is the larger blue SuperSpeed Type-B – carrying 5 Gbps. A USB 3.0 B connector is physically larger than a 2.0 B, and a 3.0 B cable seats in a 2.0 B port at 2.0 speed, which is the backward-compatibility behavior that makes the 3.0 cable the safe purchase for a mixed setup.
The Color Code
Blue is the SuperSpeed marker – a blue A tongue or a blue B shell is the USB 3.0 version of the connector. A black or white B cable is USB 2.0. The color is the fastest way to tell the two versions apart at the shelf, and it is the line to verify on a datasheet for a bulk purchase.
The Devices That Take a B Port
The Type-B port is the device-side standard for a specific set of equipment. Printers – the dominant use, from inkjet to laser – are the reason the B cable is a household part. Scanners and some multifunction devices share the port. External hard drives and SSDs of the 3.5-inch desktop class often use the full-size B, while the 2.5-inch portable class moved to the smaller Micro-B. Some audio interfaces, older docking equipment, and lab instruments keep the B port. If the device’s port is the squarish B shape, the A to B cable is the connection – in the 2.0 or 3.0 version matched to the device’s rating.
What the A to B Cable Cannot Do
The limit that matters is the one buyers test: an A to B cable cannot transfer data directly between two computers. The B end is a device port, not a host port, and the cable has no transfer chip – so two PCs joined by an A to B (or an A to A) cable have no protocol to negotiate, and the direct host-to-host connection can draw current in a way that damages the ports. A direct PC-to-PC transfer needs a USB bridge cable with a transfer controller, a network connection, or a shared drive – not a standard A to B cable. The A to B cable does one job: connect the host to the B-port device, at the speed the device and the cable both support.
USB A to B Cable: Version Comparison
| Attribute | USB 2.0 A to B | USB 3.0 A to B |
|---|---|---|
| A-end connector | 4-pin Type-A | 9-pin Type-A (blue) |
| B-end connector | 4-pin Type-B | 9-pin SuperSpeed Type-B (blue) |
| Data rate | 480 Mbps | 5 Gbps (SuperSpeed) |
| Typical use | Printers, scanners | USB 3.0 printers, 3.5″ drives |
| Backward compatible | n/a | Seats in 2.0 B at 2.0 speed |
Real-World Application Scenarios
Typical scenarios: an office printer connected to a workstation on a 1.5-meter A to B cable; a home inkjet at the desk on a short A to B run; a USB 3.0 laser printer where the blue 3.0 A to B cable carries the faster link; a scanner or multifunction device sharing the printer’s connection standard; a 3.5-inch external drive on its B-port link to a tower; and a lab or instrument rack where the B port is the device-side standard.
Recommended Internal Resources
Editorial Note: Internal linking recommendation: (1) Product cluster – https://zh-zong.com/productlist/ (anchor: explore factory-certified USB A to B cables in USB 2.0 and 3.0 versions and lengths); (2) Related guide – https://zh-zong.com/video-usb-adapter-converter-guide/ (anchor: video and USB adapter/converter guide for host-to-device USB connections); (3) Conversion – https://zh-zong.com/contact/ (anchor: contact the sales engineering team for A to B cable programs with the version and length stated per SKU).
Frequently Asked Questions (FAQ)
Q: What is a USB A to B cable used for?
A: It connects a computer’s Type-A port to a Type-B device port – the standard link for printers, scanners, and some external drives. It is a host-to-device cable, available in USB 2.0 and USB 3.0 versions.
Q: Can I use a USB A to B cable to connect two computers?
A: No. The B end is a device port and the cable has no transfer controller, so two PCs cannot negotiate over it – and the direct host-to-host connection can damage the ports. Use a USB bridge cable, a network, or a shared drive for a PC-to-PC transfer.
Q: How do I tell a USB 3.0 A to B cable from a 2.0 one?
A: By the color and the connector size – the 3.0 version has a blue A tongue and a larger blue B connector, and it carries 5 Gbps. A black or white B cable is USB 2.0 at 480 Mbps.