Technology Training

All about USB ports

The typical PC from the early 1990’s sported LPT, Serial, PS2, SCSI and MIDI ports. To name but a few! Now we have the Universal Serial Bus

USB Versions & Speeds

It’s important to understand that although two USB ports and cables might look identical, it doesn’t mean they have the same capabilities. That’s because USB standards have improved over the years. The hardware that sends and receives information is faster and the internal wiring differs significantly.

Yet, a key part of USB is the “universal” bit. In practice this means that if a USB cable fits into a port, it will work. The worst that can happen is that it defaults to the oldest, slowest standard that both devices can understand. Which means that some devices simply won’t work properly because they can’t push data through the cable quickly enough.

When you buy a USB peripheral, it will specify which the highest standard is that it supports and – sometimes – requires. That means the computer, the cable and the device must all comply with that particular USB standard for it to run as well as possible.

Right now there are three generations of USB out in the wild, with a fourth due to released in mid 2020. This is the least you need to know:

  • USB 1 has a maximum theoretical speed of 12Mbps (megabits per second). These old devices will work with current modern USB, but at no more than that speed and usually a lower one. It’s also referred to as “Full Speed” USB, which can be confusing.

White Type A USB 1.x plug

This was the first specification for USB and was released in 1996. It had some issues with extension cables / hubs and wasn’t widely adapted. It wasn’t until version 1.1 in 1998 that it started to be used in manufacturing devices. Normally white connectors are USB 1.x, but quite a few are USB 2.x compatible. The transfer rate for USB 1.X was kind of slow at only 12 Mbps (megabit per second).


  • USB 2 is way faster, with a maximum theoretical speed of 480Mbps. The marketing name for USB 2 is “High Speed”.

Black Type A USB 2.x plug

This is the second specification for USB and was released in 2000. It was labeled ‘Hi-Speed’ because it had a maximum transfer rate of 480 Mbps (megabit per second). It is completely backward compatible with USB 1.x.


  • USB 3 is the most recent standard at the time of writing and has a theoretical speed of an astonishing 5 Gbps (gigabits per second). Its marketing name is “SuperSpeed”.

Blue Type A USB 3.x plug

This is the third specification for USB and was released in 2008. It defines a new SuperSpeed mode, with transfer speeds up to 5 Gbps (gigabit per second). It is completely backward compatible with USB 2.x.


Red Type A USB Sleep and Charge plug

This is not a USB specification, but more of a feature. This color indicates that the connector does not power off during sleep or standby mode. On laptop or desktop computers they are great for charging external devices like smartphones. Its specification can be any of the above, so check your computer or device documentation for the exact one.

USB 1.1 is actually the most widely-adopted USB 1 standard, with virtually no USB 1.0 devices making it into the hands of users. USB 2.0 received a single revision, but USB 3 has had the most revision work with USB 3.1 and 3.2.

These are further divided into generations. USB 3.1 has a Gen 1 and Gen 2 subdivision. USB 3.2 has Gen 1,2 and 2×2.

The generational versions are actually significantly different in performance. USB 3.1 Gen 1 runs at 5 Gbps, but Gen 2 doubles that! The USB 3.2 generations run at 5,10 and 20 Gbps respectively.

USB Port Types

Now that we’ve covered the different USB generations, let’s talk about the actual physical ports. Before we do that however, here’s a quick tip – USB 3 ports are conventionally blue inside! That makes it easy to tell them apart from older USB port types.

The original USB port is known as the Type A port. This is the port type we all know and love, which can be found on everything from flat-panel TVs to clock radios. USB 1 and USB 2 Type-A ports have just four pins internally. Two for data and two for power. USB 3 Type-A ports have nine pins in total, but are completely backwards-compatible.

Next we have the less common Type B port. These are usually seen on devices like printers or external hard drives. It’s a female port for devices that aren’t “host devices” like a computer is. Type B USB 1 and 2 ports are not physically compatible with USB 3 Type-B ports.

Lastly, we have the latest Type-C port. This tiny, densely-wired port is reversible. Which means that unlike Types A or B ports, you can insert it any way around. With an adapter, this is compatible with all USB except for USB 1. It replaces other connection types as of USB 3.2 onwards.

That’s it for the so-called “standard” ports, but there are “mini” and “micro” version of these for devices that are too small to handle full-sized USB-A ports. Game controllers, smartphones and other small devices can feature Mini- and Micro- versions of Type-A and Type-B ports. There are also Type-AB ports for devices that act as both a host and a peripheral.

Before USB-C ports, smartphones most commonly featured Micro-B ports. Mini-B ports can be found on devices like the PlayStation 3 controller.

While Micro-B ports are still widely in use for smartphones, power banks and most modern small electronics devices, USB-C is quickly becoming the new standard for every device that uses USB, regardless of size.

USB Power Standards

USB is more than just a way to transfer data between devices. It’s also a way to transfer power. With the exception of Apple’s mobile devices, just about every modern smartphone uses a USB port of one type or another for both charging and data.

In fact, plenty of devices that transfer no data at all still use USB for charging. One example is power banks to small toy drones. Some USB cables only carry power, lacking the wiring for data transmission. Power cables that comes with power banks are sometimes of this type.

It’s actually pretty useful to use a power-only cable to prevent virus infections of mobile devices. For example, at airports where chargers may be provided, hackers can swap them out with malware-infected devices. A so-called “data blocker” USB cable prevents that particular exploit.

In terms of the actual power that comes through a USB cable, there’s a lot of variability. However, one thing you should know is that it if you plug a USB device into a USB-compliant port, it will only draw as much power as it needs or as much power as the port can supply, whichever is lowest.

So you don’t have to worry about plugging your phone into a charger with a higher power rating than the one it came with. As long as both devices and the cable are from reputable manufacturers, it’s not something you need to think about.

What is important to know is that some USB power sources aren’t going to charge or power your device well. USB provides power according to the generation of the hardware. USB 1.0 and 2.0 provide 500mAh of current. USB 3.0 can give up to 900 mAh of juice. USB 3.1 can provide as much as 3000 mAh (3A)!

These are simply the numbers a manufacturer must comply with in order to meet the certification minimums. You’ve probably noticed that car chargers and Apple iPad chargers are often rated for 2.1A, which is not part of any USB specification. In order to make use of the extra power available, the device needs to talk to the charger to negotiate how much power it wants.

If it can’t, it will simply default to the minimum, which is usually 500 mAh. All you need to know is that the charger and device both have to support the same “quick charging” standard of power that’s to be transferred above the USB specifications.

Apart from the high power delivery of the latest USB 3 versions, all other quick charging standards are not industry-standard. So there is no guarantee that your “fast-charging” smartphone will power up at its best rate on a third-party charger.

On Android phones, for example, there will usually be a notification letting you know if the device is charging slowly or quickly, along with a time estimate.

A Final Note On USB 4

The USB 4 specification was published in late 2019 and will probably appear in devices in late 2020 or early 2021. It usually takes around 18 months for devices to come to market once a new standard is published for the first time.

The USB4 solution specifically tailors bus operation to further enhance this by enabling the further doubling of performance. Yes you heard right, double the performance (40Gbps) compared to the fastest version of USB3 which offered 20Gbps. It will use the current USB-C connection.



Categorised as Blog

Leave a comment

Your email address will not be published.