There are actually two different “speeds” at which a USB 1.1 device can run at: Low Bandwidth at 1.5 Mbps or Full Bandwidth at 12 Mbps. This is considerably slower than USB 2.0’s 480 Mbps and USB 3.0’s 5,120 Mbps maximum transfer rates.
USB 1.1 Connectors
USB Type A: These plugs and receptacles are officially referred to as Series A connectors and are the commonly seen, perfectly rectangular USB connectors. USB 1.1 Type A connectors are physically compatible with both USB 2.0 and USB 3.0 Type B connectors. USB Type B: These plugs and receptacles are officially referred to as Series B connectors and are square except for a rounding at the top. USB 1.1 Type B plugs are physically compatible with USB 2.0 and USB 3.0 Type B receptacles, but USB 3.0 Type B plugs are not backward compatible with USB 1.1 Type B receptacles.
See our USB Physical Compatibility Chart for a one-page reference for what-fits-with-what. Depending on choices made by the manufacturer, a particular USB 3.0 device may or may not work properly on a computer or other host that was designed for USB 1.1, even though the plugs and receptacles physically connect to each other. In other words, USB 3.0 devices are allowed to be backward compatible with USB 1.1 but are not required to be so. Aside from incompatible issues, USB 1.1 devices and cables are, for the most part, physically compatible with USB 2.0 and USB 3.0 hardware, both Type A and Type B. However, no matter what newer standard some part of the USB-connected system supports, you’ll never reach a data rate faster than 12 Mbps if you’re using even one USB 1.1 part.
More Information on USB 1.1
The introduction of USB 1.1 is what led to computers lacking a floppy drive and legacy ports, sometimes called “legacy-free PCs.” USB 1.1 (as well as 1.0 and 2.0) uses a “speak-when-spoken-to” protocol. This means each device communicates with the host upon the host’s request. This is different from the device starting communication from itself, which is supported in USB 3.0. Per the USB 1.1 standard, low bandwidth devices (like keyboards and mice) can use a cable as long as 9 ft 10 in (3 meters). Full bandwidth devices can have a cable the same length high speed USB 2.0 devices support: 16 ft 5 in (5 meters).
