It was 1997 when it began to hear about a single connector that would be able to connect different types of devices to computers using only one type of cable and one respective port.
It is so that, as time passes, ports like COM (often used for modems and other types of devices), LPT (for printers) and PS2 (usually for mouse and keyboard) have practically disappeared and have left the place to a type of port – and its connector – of which today you could not do without: the Universal Serial Bus , which we all know in confidence as USB.
Despite all we have clearly what is a USB port and cable, it is not always clear the difference between the standards that have happened over time: leaving the standard 1.1, now fallen into disuse, in this article we will find out what is the difference between USB 2.0 and USB 3.0.
Our guide will analyze those that are the practical differences between the two standards, leaving voluntarily what concerns the part of circuitry and electronic design. Finally we will analyze the latest generation of USB, ie USB 3.1 with its USB connector Type-C, which aesthetically distinguishes from the previous but that retains some backward compatibility.
Step 1: Aesthetic differences
It is usually read that a device is equipped with a number of USB 2.0 ports and USB 3.0 ports: As these may seem identical, you will discover later that the USB devices of the two categories are capable of transmitting data at different speeds, as well as absorbing a different amount of electricity (and thus feeding different types of devices).
Aesthetically distinguishing a USB 2.0 port from a USB 3.0 port is simple: the classic plastic plate of the first is grey or black white, while the second one is blue or dark blue.
As for the cables, however, if the plastic plate is blue it is certainly a USB 3.0 – while for the white plate It may also be a USB 2.0 cable.
Step 2: Energy required for power supply
To decree the big success of USB connectivity was certainly the possibility of many devices compatible to feed “alone” simply using that type of connection, going in fact to eliminate the need for an alternative electricity source (and therefore another, annoying cable).
The Power + connection combination is born in USB 2.0 and also remains in USB 3.0, but with different numbers: USB 2.0 devices can absorb a maximum current of 100 ma, while USB 3.0 can absorb a maximum current of 150 ma.
These values change considerably during the enumeration phase – the one in which the host (the operating system) identifies the type of device connected to the port: USB 2.0 devices at that stage can absorb current up to 500 MA, USB 3.0 devices can also reach 900 ma.
So, in conclusion, USB 3.0 differs from its predecessor also due to the significant increase in the power that the devices need – USB 2.0 can feed devices up to 2.5 W USB 3.0 comes up to 4.5 w (compared to 5v input)-although specific energy optimization mechanisms are under way.
Step 3: Data transfer performance
According to the standard USB 2.0 (which we remind you to have the beauty of 14 years) the maximum theoretical transfer speed is equal to 480 Mbit/s, while that of USB 3.0 (which has “only” 4 years) is more than ten times higher, or 5 Gbit/s.
Although for some types of devices this difference is quite remarkable right from the start, it is practically impossible for a USB device to actually communicate with the host using the maximum theoretical speed due to the structural limitations of the device itself.
For example, speaking of USB storage devices (which are disks, USB sticks or flash memories), the performance of the memory type itself will affect the performance of USB, preventing the attainment of the maximum transfer rate.
However, this does not take away that the difference between USB 2.0 and USB 3.0 is perceived in the vast majority of cases, and this also decreed a slight difference in price – USB 2.0 devices are generally cheaper than USB 3.0.
Step 4: Backward compatibility
It seems obvious but in reality it is not at all: unlike what happens normally, you can use – with obvious limitations – both USB 2.0 devices in USB 3.0 ports is the opposite, without any compatibility issues. Both standards are absolutely compatible with each other regarding data transfer.
Clearly this will affect performance: a US device
The speech becomes slightly different regarding the current: No problem for USB 2.0 devices connected to the 3.0 ports, which will surely receive the quantity of current required; Different instead the opposite scenario: a USB 3.0 device may fail to get the power to power itself when connected to a USB 2.0 port, although this scenario is rarely found.
However, it should be stressed that USB 3.0 is interrupted compatibility with USB cables and MicroUSB 2.0 type A.
The USB 3.1 specification was presented last December 2013, and with it all its innovations and improvements in terms of energy and data transfer speed: First, USB 3.1 allows you to power devices with up to 100w (in some Chromebooks and the last Macbooks the USB 3.1 connector feeds and recharges the batteries and the same devices) , secondly, the achievable theoretical velocity becomes ten times higher than that of its predecessor, touching the 10 Gbit/S.
The most interesting novelty, however, is the connecting cable – deeply different from its predecessors – which today is on more and more devices: The USB Type-C connector has a thickness equal to that of a current microUSB, it is slightly longer and – very, very pleasing – is double-sided, i.e. it can be inserted into the door in both ways eliminating the danger of damaging it by incorrectly inserting it , which – strange, but true – has happened and happens quite often today with USB cables 2-3.0.
The USB Type-C connector is backwards compatible with USB 2.0-up ports, but not vice versa. Today, hybrid adapters and cables (USB 3.0 Type-B – USB 3.0 Type-C) are extremely popular to make the gradual transition from one standard (and its dedicated cable) to the other less “traumatic”.
