How fast is USB 3 0

USB 3.0 / 3.1 / 3.2 / SuperSpeed ​​USB

USB version 3.0, 3.1 and 3.2 is a universal interface with data rates of 5, 10 and 20 GBit / s.
With a speed increase to 5 GBit / s or 600 MByte / s, USB 3.0 is mainly suitable for the operation of external mass storage drives. USB 3.1 and 3.2 are mainly of interest for the connection between a notebook and a docking station or hub, where communication between several peripheral devices should take place via one connection.

The specifications for USB 3.x introduced the ability to provide power, data transfer and the transfer of video signals over a single cable. Unfortunately, the separation of the individual technical solutions has not been implemented properly.

Although version 3.0 and 3.1 in particular have many innovations, the focus is on downward compatibility. The USB 3.x host consists internally of a USB 2.0 and USB 3.x part. This ensures compatibility with older devices with USB 1.1 and 2.0.

Comparison: USB

interfaceUSB 2.0 USB 3.0 (Gen 1)USB 3.1 (Gen 2)USB 3.2 (Gen 2x2)
Transfer rate
(theoretically)
480 Mbit / s5 GBit / s10 GBit / s20 GBit / s
up to 60 Mbytes / s up to 600 Mbytes / sup to 1,200 MB / s2 GB / s
Transfer rate
(practically)
approx. 30 MB / sapprox. 450 Mbytes / sapprox. 800 MB / sapprox. 1.6 GB / s

Transmission speed

The first digit before or without “x” can be Gen 1 (5 Gbit / s), Gen 2 (10 Gbit / s) or Gen 3 (20 Gbit / s). The second digit after the "x" tells you how many high-speed wire pairs are connected. Without this information, it is just a pair of wires.

USB 3.2 Gen 1 with 5 GBit / s (USB 3.0)

USB 3.2 Gen 1 (USB 3.0) achieves a mathematically maximum transfer rate of 500 MByte / s. In the classic BOT transmission mode (Bulk Only Transport), however, only achieves approx. 250 Mbytes / s. About twice as fast, approx. 450 MB / s, is only possible with the USB Attached SCSI Protocol (UASP). All modern operating systems automatically support this, provided the host adapter in the storage device also supports it. But that doesn't help if, for example, the external hard drive does not exceed 200 MB / s.

Note: USB 3.0 may also be called "USB 3.2 Gen 1" and then does not support 10 GBit / s, but only 5 GBit / s.

USB 3.2 Gen 2 with 10 GBit / s (USB 3.1)

USB 3.2 Gen 2 (USB 3.1) specifies a transfer rate of 10 GBit / s, for both type A and type C connectors.
The doubling of the speed from 5 to 10 GBit / s is possible without new connectors, protocols or drivers. In addition, instead of 20 percent overhead, thanks to more efficient coding (128b / 132b instead of 8b / 10b), only 3 percent is lost. The bottom line is that this should result in a transfer rate of around 1 GByte / s. In practice you get about 800 MB / s. That is more than with SATA-6G with a maximum of 600 MByte / s. However, the full transfer rate can only be achieved here if all parties involved (host adapter, device, hubs) have mastered this transfer mode.

In practice you have to note that if a device says USB 3.1 or 3.2 on it, it does not necessarily support 10 GBit / s (USB 3.2 Gen 2). It can also only be 5 GBit / s (USB 3.2 Gen 1).

Note: The name “SuperSpeedPlus” for USB with 10 GBit / s has been abolished, although the word “SuperSpeed ​​+” and the associated logo still exist. A distinction is made between USB 3.2 Gen 1 and USB 3.2 Gen 2.

USB 3.2 Gen 2 × 2 with 20 GBit / s

The doubling of the data rate of a link (connection) to 20 GBit / s with USB 3.2 is done by a second pair of wires in the USB cable with type C connector.
While the previous versions only used a differential pair of wires from the USB-C cable, USB 3.2 Gen 2x2 allows two wire pairs to be used in dual-lane or multi-lane operation, each with 10 Gbit / s per direction. So a total of 20 GBit / s.
The multi-lane technology also works with USB 3.1, i.e. two 5 GBit / s transfers in parallel on two pairs of wires each and thus a total of 10 GBit / s.
However, this also means that to use both wire pairs you need a cable with a USB-C connector at both ends and there are restrictions with regard to the cable length and parallel use. For example, if the second pair of wires is used for USB-C docking with DisplayPort, then a connection is only possible with a link. With USB 3.2 then only with a speed of 10 GBit / s.

Note: If a manufacturer wants to offer more than the USB 3.1 with 10 GBit / s that has so far been integrated into CPUs or chipsets, USB4 is the better choice. As with USB4, the use of USB 3.2 with 20 GBit / s requires a cable with a USB Type-C connector. And the lowest common denominator in USB4 is the speed of USB 3.2.

Plug connection for USB 3.0, 3.1 and 3.2

The SuperSpeed ​​mode only works with USB cables which, in addition to the previous data line pair (D + / D-), have a separately shielded wire pair (Shielded Differential Pair, SDP) for both transfer directions, as well as a common shield to comply with EMC limit values of the entire cable.

Instead of cable lengths, the USB specification defines limit values ​​for the electrical parameters at which the transmission functions reliably. The typical cable length should be 3 meters. Particularly good, but also expensive cables should achieve more.
Type A connectors, which are suitable for USB 3.0 and 3.1, can be recognized by the blue colored inner part. Older USB cables are usually white or black inside.

The type A plug for USB 3.0 and 3.1 has five additional contacts, with the type A plug being compatible with the old USB sockets. In the type A plug, the new contacts are in the area where there is only plastic in the old plug. The advantage here is that all type A plugs and sockets fit together. It looks different with micro USB and type B plugs. Here the connector gets an attachment that accepts the additional pins. This means that the connection has a USB 2.0 and a USB 3.0 part. This means that old plugs fit into the new sockets, but not the other way around. There is no space for a USB 3.0 device plug in a USB 2.0 device socket. If you only have one USB 2.0 cable for a USB 3.0 device, then the device can only be operated at USB 2.0 speed.

Compatibility is also retained with USB 3.1. Only the electrical conditions for shielding and grounding have been adjusted. The cables should then usually only be 1 meter long. Longer cables are unsuitable for speeds of 10 GBit / s or more.

Note: The plug connection has no influence on the speed. USB 3.1 does not need the USB-C connector. It is only important that the controller behind the socket supports USB 3.1. The USB-C connector is only required from USB 3.2 onwards, because the higher speed is achieved here by using additional wire pairs.

Data transfer

The main criticism of the USB is the polling during data transmission. The host asks all devices again and again whether they have data to transfer. As of USB 3.0, the individual devices can report with "Not Ready" (NRDY) that they want to respond to the query later. The host remembers this and no longer queries these devices. But as soon as a device has data to transfer, it reports "Endpoint Ready" (ERDY). This is intended to make the data transfer more efficient.
USB 3.0 provides for further measures to increase the efficiency of data transfer. The 5 GBit / s flow over two new wire pairs. The USB controller sends data to the device via SSTX + and SSTX- and data flows back via SSRX + and SSRX-. Since USB 3.0 separates send and receive lines, a device does not have to wait for the bus to be allocated by the controller. If the controller receives an ERDY, it queries the device as with USB 2.0. The advantage of this approach is that the controller logic is responsible for it. The overlying logs do not notice this process.

Power supply

For USB 3.x devices, the 100 mA limit is raised to 150 mA in low power mode. In high power mode, the 500 mA limit is raised to 900 mA. The chances of eliminating the problematic Y-USB power adapters and additional external power packs are good.

Power saving mode

The NRDY signal has another advantage. If a device has sent an NRDY, it can switch itself to a power-saving mode. If all devices connected to the controller do this, then the controller can also switch its upstream link to power-saving mode. This is particularly interesting for battery-operated devices.

USB 3.x knows four power saving modes:
  • U0 = optional
  • U1 = switched on PLL
  • U2 = switched off PLL
  • U3 = Suspend

USB authentication (USB with signature)

Part of USB Version 3.1 is USB device authentication. USB devices can identify themselves to a USB host with a digital certificate. USB-C devices can identify each other via cryptographic functions and certificates. The aim is to avoid manufacturers who, for example, only use their own chargers on their devices from developing proprietary solutions, but being able to implement them using certificates.

Problem: USB 3.x devices interfere with WLAN and Bluetooth connections

WLAN and Bluetooth connections can be disturbed by USB 3.x devices. The problem is because the base frequency for SuperSpeed ​​mode of 5 GT / s is 2.5 GHz, which is near the 2.4 GHz frequency range. This frequency range is used by WLAN, Bluetooth and other local radio systems. The USB base frequency is emitted by cables, connectors and devices. Even if the components have good shielding. In any case, an inappropriately placed USB 3.x device can interfere with WLAN and Bluetooth devices.

In the short term, the problem can be solved by connecting USB 3.0 devices with a very short and well-shielded cable or by increasing the distance to the radio devices. In addition, it makes sense to operate a WLAN in the 5 GHz band.

Overview: USB - Universal Serial Bus

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Everything you need to know about computer technology.

Computer technology primer

The computer technology primer is a book about the basics of computer technology, processor technology, semiconductor memories, interfaces, data storage devices, drives and important hardware components.

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