USB (Universal Serial Bus) is a standard interface used for connecting peripherals to a computer or other device. There are different USB formats that refer to the speed and performance capabilities of the USB connection.
USB Formats Overview
The main USB formats are:
- USB 1.0 – Released in 1996, supports speeds up to 12 Mbps.
- USB 1.1 – Released in 1998, minor revision to USB 1.0.
- USB 2.0 – Released in 2000, supports speeds up to 480 Mbps.
- USB 3.0 – Released in 2008, supports speeds up to 5 Gbps.
- USB 3.1 – Released in 2013, supports speeds up to 10 Gbps.
- USB 3.2 – Released in 2017, supports speeds up to 20 Gbps.
- USB4 – Released in 2019, supports speeds up to 40 Gbps.
The USB formats with higher numbers represent newer versions of the USB specification with faster maximum speeds. Each version is compatible with previous USB formats – for example, a USB 2.0 device will work on a USB 1.1 port.
What is USB Full Speed?
USB Full Speed refers specifically to the USB 1.1 specification, which supports a signaling rate of 12 Mbps. This was the fastest speed supported by the original USB 1.0 specification released in 1996.
The term “Full Speed” is used to distinguish USB 1.1 from the original “Low Speed” USB 1.0, which only supported a signaling rate of 1.5 Mbps. So Full Speed USB offers nearly a 10x increase in the maximum bandwidth over Low Speed USB.
Full Speed vs High Speed USB
Here is a comparison between Full Speed USB and High Speed USB:
| Specification | Full Speed USB | High Speed USB |
|---|---|---|
| Official Name | USB 1.1 | USB 2.0 |
| Year Released | 1998 | 2000 |
| Signaling Rate | 12 Mbps | 480 Mbps |
| Maximum Power | 500 mA | 500 mA |
| Connectors | Type A, Type B | Type A, Type B, Mini-B |
As the table shows, High Speed USB offers a major increase in maximum bandwidth compared to Full Speed – 480 Mbps vs. 12 Mbps. However, Full Speed and High Speed use the same power supply capabilities and similar connectors.
Advantages of Full Speed USB
Here are some of the advantages of Full Speed USB:
- Compatible – Works with a wide range of USB 1.0 and 1.1 devices.
- Ubiquitous – Supported on nearly all computers and operating systems.
- Inexpensive – Full Speed devices are widely available and cost-effective.
- Good Enough Speed – 12 Mbps is satisfactory for many peripherals like keyboards, mice, and gamepads.
- Low Power – Uses less power compared to higher speed USB 3.0+ devices.
In summary, Full Speed USB offers very broad compatibility with USB 1.0/1.1 devices, good enough speeds for many peripherals, and low cost – all useful traits for legacy support.
Disadvantages of Full Speed USB
Here are some of the disadvantages of Full Speed USB:
- Slow maximum speed – Limited to 12 Mbps signaling rate.
- Not suitable for high-bandwidth devices – Like external storage, HD cameras, audio interfaces.
- Limited cable length – Max 16ft without signal boost.
- No interrupt signaling – Only bulk endpoint transfer type supported.
- Less common now – Most modern devices use USB 2.0 or 3.0.
In summary, Full Speed USB is quite slow by today’s standards. It works fine for mice and keyboards but cannot handle transfer-intensive devices requiring High Speed or SuperSpeed USB.
Typical Uses of Full Speed USB
Here are some of the most common uses and applications of Full Speed USB:
- Computer keyboards and mice
- Gamepads and joysticks
- Barcode scanners
- Printers and scanners
- POS and cash register systems
- USB hubs and extension cables
- Embedded systems and microcontrollers
Full Speed USB is well suited for human interface devices like keyboards and mice that don’t require high bandwidth but need broad compatibility. It also sees use in point-of-sale systems, printers, and other applications where High Speed USB may be overkill.
Full Speed USB Cable Length Limits
The maximum cable length for Full Speed USB is limited to around 16ft (5m). This is because USB 1.1 uses unshielded twisted pair cabling which is susceptible to signal degradation over longer distances.
There are a few ways to work around this 16ft limit:
- Use self-powered USB hubs – The hub will regenerate the digital signal.
- Use USB extension cables – Active cables with signal boost circuitry built in.
- Use USB repeaters – Devices to regenerate and amplify the USB signal.
With one or more of these USB range-extending devices, you can transmit Full Speed USB signals to lengths of 100ft or more. Just keep in mind that chaining too many extenders can lead to potential signal errors or reduced reliability.
Migration from Full Speed to Higher USB Speeds
For new devices requiring high bandwidth, it’s recommend to use USB 2.0 High Speed or faster connections rather than Full Speed USB. However, many devices still need to maintain compatibility with legacy Full Speed USB.
Here are some tips for migrating from Full Speed to faster USB versions:
- Use USB 2.0 if the device bandwidth needs are between Full Speed and High Speed.
- Support USB 3.0+ in new designs for maximum future-proofing.
- Use USB Type-C connectors for reversibility and orientation-free operation.
- Include USB 2.0 support for backwards compatibility with USB 1.1 hosts.
- Utilize USB 3.0+ only when the speed is truly needed for the application.
With smart design decisions, you can migrate devices to faster USB speeds while maintaining backwards compatibility with the massive number of older Full Speed USB hosts and peripherals still in use.
Conclusion
In summary, Full Speed USB refers to the USB 1.1 specification supporting signaling rates up to 12 Mbps. While quite slow by modern standards, Full Speed USB still offers the advantages of very broad compatibility, good enough performance for many basic peripherals, and low cost.
However, for applications requiring high bandwidth, it is recommended to use faster versions of USB such as USB 2.0 High Speed or USB 3.0 SuperSpeed. With careful planning, devices can migrate to faster USB speeds while maintaining backwards compatibility with the legacy ecosystem of Full Speed USB 1.1 hosts and devices still prevalent today.
