| USB4 | |
| Type: | USB |
| Designer: | USB Promoter Group |
| Superseded: | USB 3.2 |
| Daisy Chain: | No |
| Maximum Voltage: | 48 V (PD 3.1) |
| Maximum Current: | 5 A (PD) |
| Audio Signal: | DisplayPort |
| Video Signal: | DisplayPort |
| Data Signal: | Yes |
| Data Bandwidth: | 20 Gbit/s 40 Gbit/s 80 Gbit/s 120/40 Gbit/s asymmetric |
| Physical Connector: | USB-C |
USB4 (Universal Serial Bus 4), sometimes erroneously referred to as USB 4.0, is the most recent technical specification of the USB (Universal Serial Bus) data communication standard. The USB Implementers Forum originally announced USB4 in 2019.
USB4 enables multiple devices to dynamically share a single high-speed data link. USB4 devices must support a data communication bit rate of at least 20 gigabits (Gbit/s). The current version allows bit rates of 40 Gbit/s (since USB4 version 1.0) and 80 Gbit/s (since USB4 version 2.0).[1] USB4 is only defined for the USB-C connector and its Type-C specification regulates the connector, cables and also power delivery features across all uses of USB-C cables, in part with the USB Power Delivery specification.
The USB4 standard mandates backwards compatibility to USB 2.0, USB 3.x and DisplayPort connections.The dynamic sharing of bandwidth of a USB4 connection is achieved by carrying virtualized "tunnels" of other connections. This includes tunneling of USB3 and connections. Other protocols, such as PCI Express and Ethernet can also be tunneled, even without a way to access these directly, directly from USB4 ports.
USB4 also incorporates some elements and shares principles with the Thunderbolt 3 protocol; however, interoperability with Thunderbolt 3 products is mandatory only for select USB4 device types.
Prior to USB4, Thunderbolt provided a way to dynamically share bandwidth between multiple and PCIe connections over a single cable. Thunderbolt originally used the mDP connector and was only backward compatible to connections and did not support power transfer.
The introduction of the Type-C connector in 2014 provided a connector that could support both USB data connectivity, power transfer as well as connections. It also allowed the static sharing of bandwidth between DP and USB connections over the same cable.
Thunderbolt 3 switched over to using the new Type-C connector and also added backwards compatibility for USB connections and power transfer features.
USB4 was announced in March 2019.[2] [3] The USB4 specification version 1.0, released 29 August 2019, uses "Universal Serial Bus 4" and specifically "USB4", that is, the short name branding is deliberate without a separating space, which is different from prior versions. Several news reports before the release of that version use the terminology "USB 4.0" and "USB 4".[4] [5] Even after publication of rev. 1.0, some sources write "USB 4", claiming "to reflect the way readers search".[6]
At time of publication of version 1.0, promoter companies having employees that participated in the USB4 Specification technical work group were: Apple Inc., Hewlett-Packard, Intel, Microsoft, Renesas Electronics, STMicroelectronics, and Texas Instruments.
Goals stated in the USB4 specification are increasing bandwidth, helping to converge the USB-C connector ecosystem, and "minimize end-user confusion". Some of the key areas to achieve this are using a single USB-C connector type, while retaining compatibility with existing USB and Thunderbolt products.[7]
On 1 September 2022, the USB Promoter Group announced the pending release of the USB4 Version 2.0 specification, and the specification was subsequently released on 18 October 2022.[8] [9] It added 80 Gbit/s speeds with optionally asymmetric connections, a new, optional alternative to the existing "USB3 Gen T tunneling", removed PCIe overhead limitations and updated the support of DisplayPort to the then current Version 2.1.
Around the release of the new USB4 Version 2.0 specification, USB-IF also transitioned to new logos and names to simplify representing the maximum supported speeds (and wattages) to consumers.[10] The new names are unified across all USB standards and removed the prior, explicit distinction between "SuperSpeed USB 20 Gbps" and "USB4 20Gbps" connections.
Similarly to how USB 3.x defined the new SuperSpeed protocols for faster connections, but also mandated that any USB3 port still include the pins and functionality for the previous USB2 connections, the USB4 specification describes 2 different aspects. The first one is what type of existing connections and compatibility a USB4 port guarantees. Since USB4 uses the Type-C connector, which was designed to be multifunctional and reversable, the term "host" port does not accurately reflect the situation. This is better denoted as a downward facing port (DFP). The peripheral side can similarly be described as upward facing port (UFP).
Any downward facing USB4 port is required to also implement USB 2.0, USB 3.2 and DP Alt mode support. Each according to their own specifications. As such a USB4 is backwards compatible to all previous USB devices.
The USB2 family currently defines 3 different speeds (Low-, Full-, High-Speed), all are required to be supported. The newest available version of this specification is USB 2.0 Rev. 2.0. USB 2.0 abilities uses separate wires on the Type-C connector that are not used by USB 3.2 or USB4 connections. USB4, just as USB 3.2 before provides a parallel USB 2.0 connection to be present on the same cable to support backwards compatibility to USB 2.0 modes.
The USB3 family currently defines 3 different modes and therefore signaling rates ("5 Gbps" a.k.a. SuperSpeed, "10 Gbps" a.k.a. SuperSpeed+, "20 Gbps" a.k.a. SuperSpeed+ 20 Gbps). While the current USB 3.2 specification has been referenced since USB4 Version 1.0, only the 2 lower speeds (5 Gbit/s, 10 Gbit/s) are mandatory for USB4 DFPs to support.
The USB4 specifications make no reference to a minimum feature set for its DP Alt Mode functionality. It seems any support is enough. Although in practice, Intel's family of TB4 controllers support up to HBR3 speeds according to the DisplayPort 1.4a specification and DisplayPort Alt Mode specification.[11]
The USB4 specification makes no explicit demands on power output. It outsources all requirements in terms of power to the Type-C specification that underpins all USB, Vesa and other standards that use the USB-C connector. This requires a USB4 DFP to supply at least 7.5W Type-C current. No power consumption features (e.g. charging of a notebook) are required, but can of course be supported following the USB PD specification. as well as supplying considerably more power. The USB PD protocol must always be supported (exchanging data according to the protocol. This is separate from any functionality of PD to negotiate actual power delivery other than 5V or > 15W).
Every USB4 port must support the new USB4 protocol, at least with the minimum speed of 20 Gbit/s.
USB4 Hubs and Docks are defined as their own category of USB4 devices, that include further requirements. For example, a USB4 Hub must also serve as a classic USB 3.2 hub with DP Alt mode passthrough with hosts that do not support USB4 connections.See USB4 Features by Device Type for more details.
Every USB4 port must support the USB4 protocol / connections, which is a distinct standard to establish USB4 links / connections between USB4 devices that exists in parallel to previous USB protocols. Unlike USB 2.0 and USB 3.x it does not provide a way to transfer data directly, but rather it is a mere container that can contain multiple "tunnels" / virtual connections.
Other specifications are referenced to define the contents and internal functionality of a tunnel. USB4 defines the following tunnel types:
USB4 forms a tree-like topology of USB4 routers (each USB4 device includes a USB4 router to participate in this network). A tunnel can be end-to-end, where the route through the entire network of routers is preconfigured. But tunnels can also be single-hop, where it exists only for a single USB4 link (between 2 routers). In this case the tunnel will be "unpacked" by the recipient and will use some other, tunnel type specific means to identify where the data needs to be sent next. If the next hop is another USB4 router, the data will be ingested again into the next single-hop tunnel until it exits the USB4 network.
Accordingly, single-hop tunnels require specific support in each USB4 router to support even passing them through to further USB4 routers. End-to-end tunnels however only require specific support at the USB4 router where the data is ingested into the tunnel and at the target, the point where the tunnel ends.
A Protocol Input Adapter will ingest a connection according to whatever protocol it is based on and convert the contents into a USB4 tunnel. Protocol Output Adapters do the reverse. They extract a tunnel from the USB4 network and if needed recreate a regular connection from the tunnel contents.
The conversion into a tunnel typically entails removing any Phy/Electrical layer and encoding of the underlying connection standard and potentially losslessly compresses the contents, for example by leaving out empty filler data. A USB4 tunnel itself is virtual and need not conform to any fixed bandwidth or other limitations that stem from the Phy/Electric layer of the underlying connection standard. But since most tunnel types will eventually be converted back to a regular, physical connection again, most of those physical limitations, like max. bandwidth are still likely to apply in the end.
This is a single-hop tunnel that essentially can transport any Enhanced SuperSpeed connection according to the USB 3.2 specification. USB3 Gen X follows the Enhanced SuperSpeed Hub topology, where every USB4 router with more than one USB3 endpoint must include a USB3 hub as well. It is the default way USB3 connections through USB4 are made. Supporting it at 10 Gbit/s (SuperSpeed USB 10 Gbps, Gen 2x1) is mandatory on every USB4 . The minimum supported speed for the USB3 connection being tunneled is 10 Gbit/s as every USB4 device already has to support this speed and USB3 Hubs handle converting this to 5 Gbit/s devices that may be connected.
This means, that a USB4 Hub will share a single upstream USB3 connection and distribute its bandwidth across all its downstream facing ports that make use of USB3 connections.
This is an optional alternative to USB3 Gen X tunneling that was introduced in USB4 Version 2.0. It is an end-to-end variant of USB3 Gen X tunnel.
Through this, it eschews the need for USB3 hubs in every USB4 router that can and will limit the throughput. It allows multiple separate USB3 Gen T tunnels even over shared links. Since it is an end-to-end tunnel, every USB4 hub will support passing it through. USB3 Gen T is intended as exclusively virtual, there exists no physical equivalent for it. Thus, it can only be used inside of a USB4 controller. This allows it to leave the limitations to 10 or 20 Gbit/s connections of USB 3.2 behind, while reusing most of the other parts of the Enhanced SuperSpeed protocol.
No known USB4 controller implements support for Gen T tunneling to date (August 2024).
DisplayPort is also tunneled as end-to-end connection. There can be multiple independent DP tunnels, but each will be delivered to a single protocol output adapter (at which point DisplayPort MST might be used to further split each connection up).
USB4 Version 1.0 only defines how to tunnel DP connections according to the DisplayPort 1.4a specification (up to HBR3 speeds). USB4 Version 2.0 updates this support to the full DisplayPort 2.1 specification (up to UHBR20 speeds).
DP tunneling has great understanding of the contents of DP connections, and will efficiently skip/transmit any filler data, reducing the actually utilized bandwidth of a DP tunnel. But since DP connections have real-time requirements, bandwidth must be reserved for them. USB4 mandates that in absence of any other information, the maximum possible bandwidth for the particular DP connection (DP lanes and speed) must be reserved. This reservation only applies to other real-time tunnels though. Reserved, but unused bandwidth can be used by non-real-time tunnels such as PCIe or USB3, but the reservation may still block other DP tunnels from being established.
Similar to USB3 Gen X tunneling, PCIe tunneling uses single-hop tunnels, requiring PCIe switches in every USB4 router that supports PCIe tunneling. USB4 has, from the start, referenced the PCI Express Specification Revision 4 and with USB4 Version 2.0 added references to PCI Express Specification Revision 5.0
PCIe tunneling has had a significant limitation in USB4 Version 1.0 and also Thunderbolt 3: PCIe Express has a variable maximum payload size, which applies end-to-end to a transmission. If any one component or PCIe Switch has a limited, all packets passing through must be limited accordingly. Because USB4 uses a payload of up to 256 Byte per USB4 packet and a PCIe tunnel packet contains further PCIe headers and meta data, the MPS for PCIe tunnels was limited to 128 Byte. This limitation can reduce the efficiency of the PCIe connection greatly for all devices and systems that would otherwise support 256 Byte or even larger MPS.
USB4 Version 2.0 removes this bottleneck (mandatory for all implementers), by defining how a larger PCIe packet can be split across multiple USB4 packets. Support for this new feature requires every USB4 component / controller involved in the PCIe tunnel to implement USB4 Version 2.0.
Signaling refers to the lowest layer of the OSI Model, also called physical layer or phy.USB4 connections can be expressed with consumer facing names that are also the basis for the official logos used on packaging and products. These are the "20 Gbps", "40 Gbps", "80 Gbps" labels and they do not explicitly indicate how the connection is achieved on the physical layer.There are also more technical names based on the implementation and use of the USB-C cables. These usually consist of a speed per wire-pair expressed as Gen 1/2/3/4 (5 Gbit/s, 10 Gbit/s, 20 Gbit/s, 40 Gbit/s respectively) and some further information on how many wire-pairs are used in which combination.
USB commonly defines a "Lane" as a (bidirectional) connection, which for all recent transmission modes consists of one sending and one receiving wire-pair. The "Gen AxB" notation refers to B Lanes of operation mode A.Since Gen 4 modes also introduced asymmetric connections with uneven numbers of wire-pairs dedicated to sending and receiving, the Lane-notation is no longer applicable.
The USB 3.x family has had the same technical notation retroactively added in the USB 3.1 and USB 3.2 specification versions. Though this shows common principles and the same generations refer to the same nominal speeds, "Gen A" does not have the same exact meaning in both USB 3.x and USB4 specifications. The overlap in naming mainly becomes relevant for cables as shown in Cable Compatibility, which is regulated by the Type-C specification shared across all users of Type-C connector.
| Introduced in | Encoding | wire-pairs sending / receiving | Raw Bit Rate | Net Data Rate | USB-IF Current Marketing Name[12] | Logo | |||
|---|---|---|---|---|---|---|---|---|---|
| per wire-pair | total (per direction) | ||||||||
| High-Speed | USB 2.0 | NRZI w/ bit stuffing | 1 (shared) | 0.480 (half-duplex) | 0.480 (half-duplex) | Hi-Speed USB | |||
| Gen 1x1 | USB 3.0 | 8b/10b | 1/1 | 5 | 5 | 4 | USB 5Gbps | ||
| Gen 2x1 | USB 3.1 | 128b/132b | 1/1 | 10 | 10 | ~9,7 | USB 10Gbps | ||
| Gen 1x2 | USB 3.2 | 8b/10b | 2/2 | 5 | 10 | 8 | colspan="2" | ||
| Gen 2x2 | 128b/132b | 2/2 | 10 | 20 | ~19.39 | USB 20Gbps | |||
| Gen 2x1 | USB4 v1.0 | 64b/66b | 1/1 | 10 | 10 | ~9,697 | colspan=2 | ||
| Gen 2x2 | 2/2 | 10 | 20 | ~19.39 | USB 20Gbps | ||||
| Gen 3x1 | 128b/132b | 1/1 | 20 | 20 | ~19.39 | colspan=2 | |||
| Gen 3x2 | 2/2 | 20 | 40 | ~38.79 | USB 40Gbps | ||||
| Gen 4 symmetric | USB4 v2.0 | PAM-3[13] 11b/7t | 2/2 | ~40.58 | ~81.15 | ~80.46 | USB 80Gbps | ||
| Gen 4 asymmetric 3:1 | 3/1 | 3x: ~121.725 1x: ~40.58 | 3x: ~120.69 1x: ~40.23 | colspan=2 | |||||
| Gen 4 asymmetric 1:3 | 1/3 | colspan=2 | |||||||
| Gen 2x2 | 64b/66b | 2/2 | 10.3125 | 20.625 | 20 | colspan="2" | |||
| Gen 3x2 | 128b/132b | 2/2 | 20.625 | 41.25 | 40 | ||||
Thunderbolt 3 Gen 2 and Gen 3 and the USB4 Gen 2 and Gen 3 modes use very similar signaling, however, Thunderbolt 3 runs at slightly higher speeds called legacy speeds compared to USB4's rounded speeds.[14] Thunderbolt 3's choices leads to the marketed bandwidth being the actual net data rate (after encoding overhead is removed). USB standards have mostly marketed the raw data rate instead.
USB4 Gen 4 is normally referred to as a speed of "40 Gbps" or 40 Gbit/s, with the full connections based on it being referred to as 80, 120/40, 40/120 Gbit/s. But since the actual signaling no longer is binary, the actual raw bit rates no longer match those numbers exactly.
A USB4 Hub is defined by having 1 USB4 and one or more USB4 .
A USB4-Based Dock is defined as a USB4 hub that also has more specialized outputs like HDMI or DP, but still keeping some USB4 DFP.
A USB4 Peripheral Device is defined by not having any USB4 DFP. This means devices that are colloquially called "USB-C Hubs" may use USB4 to support the dynamic bandwidth sharing or higher bandwidths of USB4. But they are not USB4 Hubs if they do not have any USB4 DFP. Not having any USB4 DFP allows the peripheral to only support exactly those USB4 features that it has uses for, potentially simplifying its implementation by a lot.
| Host | Hub (Dock) | Peripheral device | |||
|---|---|---|---|---|---|
| Type | |||||
| USB4connection | "20 Gbps" (Gen 2x2) | ||||
| "40 Gbps" (Gen 3x2) | |||||
| "80 Gbps" (Gen 4 symm.) | |||||
| "120/40 Gbps" (Gen 4 3:1) | |||||
| "40/120 Gbps" (Gen 4 1:3) | |||||
| Tunneled < | -- Tunneled names are actually "USB3" according to the spec --> | USB3 "10 Gbps" (Gen 2x1) | |||
| USB3 "20 Gbps" (Gen 2x2) | |||||
| USB3 Gen T (variable bandwidth) | |||||
| DisplayPort | |||||
| PCI Express | |||||
| Host-to-Host communications /USB4 Networking | |||||
| native < | -- There are valid arguments for calling it USB 3.x to keep the naming scheme. I just think it makes the table needlessly verbose. You can argue for "USB 3.2" because that is what the current version of the USB4 spec references. But that would change if there ever is a newer version and it does not matter. "SuperSpeed 5 Gbps" would also be correct and follow the official language guidelines best suited for consumers and easy understanding --> | USB3 "5 Gbps" (Gen 1x1) | |||
| USB3 "10 Gbps" (Gen 2x1) | |||||
| USB3 "20 Gbps" (Gen 2x2) | |||||
| USB 2.0(Low-, Full-, High-Speed) | |||||
| DisplayPort Alternate Mode | |||||
| Thunderbolt Alternate Mode | |||||
| Other Alternate Modes |
The Type-C standard supports cable backward / downward compatibility in many situations. The compatibility typically only breaks between the different families of standards (USB&2.0, USB 3.2, USB4). The USB4 standard mandates that classic active or hybrid active cables still have vast backward compatibility support, so as to behave as if they were regular, passive cables in the eyes of the consumer. But forward compatibility is limited for active cables. Only Optically Isolated Active Cables (OIAC), that should be clearly distinguishable (price, design, cable thickness, advertising) is allowed to strip most of the backwards compatibility away.
The Gen 4 transmission mode, with PAM-3 uses very different signaling to previous modes. Every active components needs to explicitly support this new signaling. But it stays within all signal quality requirements of existing, passive Gen 3 cables (USB4 and TB3).
USB-IF intends only for the new, bandwidth-based logos and names to be used with consumers.[15] And for cables, the type (passive, active) and the highest supported bandwidth are usually enough to uniquely identify a cable and its supported features. Although some active types make clear distinctions where further details on the type are required.Formally, a cable type and properties are defined by a specific specification version, which was used during the development / design of said cable model, so each cable would be a valid and possibly certified cable according to a specific set of USB specification versions like "Type-C 2.3, USB 3.2, USB4 Version 2.0".But the standard is also designed to be interoperable, in that a newer specification version typically adds new modes of operation, new cable types, but does not restrict previously existing things. Because that would make existing things incompatible with new products. For this purpose even the older USB logos and labels did not include a specification version, but only stated "Certified USB SuperSpeed+ 10 Gbps". This logo identified cables that could support the 10 Gbit/s connection speeds of USB3 across both the USB 3.1 and USB 3.2 version, because the requirements for the cables have not changed. Thus the precise specification version is usually not relevant and would not make a difference.
Transmission modes such as Gen2x2 are also irrelevant to cables, as valid cables are either full-featured, having all the high speed wire-pairs for up to dual-lane connections at the stated speed or they are USB2-only or some other specific and restrictive type as listed below.
| Speed | Marketing Names | max. USB4 bit rate | Exp. max.Cable Length | Other Support | Power | |||||
|---|---|---|---|---|---|---|---|---|---|---|
| USB2 | USB3 | TB3 | DP | |||||||
| USB2 | Hi-Speed USB | ≤ 4m | USB PD:60W or 100W or 240W | |||||||
| Full-Featuredpassive | Gen 1 | USB 5Gbps | ≤ 2m | rowspan="2" | ||||||
| Gen 2 | USB 20Gbps(USB 10Gbps deprecated) | ≤ 1m | ||||||||
| passive (passive TB4 & TB5) | Gen 3 & Gen 4 | USB 40GbpsUSB 80Gbps | (or asymm.) | ≤ 0.8m | rowspeed="2" | |||||
| active / hybrid optical | Gen 2 | USB 20Gbps(USB 10Gbps deprecated) | < 5m | |||||||
| act./hybr. optical(active TB4) | Gen 3 | USB 40Gbps | rowspan="2" TB up to 2m | |||||||
| act./hybr. opt.(active TB5) | Gen 4 | USB 80Gbps | (or asymm.) | |||||||
| USB3 active | Gen 2 | |||||||||
| USB3 | Gen 2 | rowspan="3" | ||||||||
| USB4 | Gen 3 | rowspan="2" | ||||||||
| Gen 4 | (asymm. optional) | |||||||||
| Thunderbolt 3 passive | Gen 2 | TB Logo without "3" | ≤ 2m | [16] | USB PD:60W or 100W | |||||
| Gen 3 | TB Logo + "3" | (or asymm.) | ≤ 0.8m | |||||||
| Thunderbolt 3 active | Gen 3 | TB Logo + "3" | (longest available: 3m) | [17] | [18] | |||||
| Thunderbolt 3 optical[19] | Gen 3 | TB Logo + "3" | ||||||||
The Type-C specification does not name specific DP speeds that it considers supported for passive cables and support is optional for active cables. The USB-C presentation on DP Alt mode[20] calls out passive full-featured USB-C cables for their DisplayPort support and headroom for future DP speed increases. HBR3 was the highest available DP speed at this time.
Active cables may have additional complications, because the active electronics do not need to operate all high speed wire-pairs in the same direction for normal USB operations (but "80 Gbps" cables are mandated to support asymmetric connections, which includes at least some of the wire-pairs operating in either direction). Active cables can have further limitations as the active electronics may only support specific signaling modes. There are 2 variants of active electronics. Linear ReDrivers only amplify the signal without any particular signaling mode or encoding in mind. ReTimers explicitly reconstruct the incoming signal for a higher quality result.
TB4 cables, even active ones, at least up to 2m in length are guaranteed to support DP Alt mode. A specific max. speed is also not mentioned, but the other requirements for TB4 all refer to DP 1.4 and its max. speed of HBR3.[21] TB5 renews the same guarantee[22] for "80 Gbps" cables while referencing the DP 2.1 specification (up to UHBR20 speeds).
DP 2.1 aligned itself to the USB4 PHY layer according to Vesa, the creator of DisplayPort.[23] It is unclear how complete this alignment is, however the UHBR10 DP speed matches USB4 Gen 2 in bit rate and encoding and UHBR20 DP Speed matches USB4 Gen 3 in bit rate and encoding. A USB and DP certification service lists USB Gen 1 cables ("5 Gbps") as supporting UHBR10 speeds, which would fit for having the same requirements as USB4 "20 Gbps" connections.[24]
Anandtech reports[25] that "this also means that DP Alt Mode 2.0 should largely work with USB4-compliant cables, although VESA is being careful to avoid promising compatibility with all cables".
There are Linear Redrivers[26] and ReTimers[27] available that are advertised for USB4 Gen 3 speeds and all current DP speeds up to UHBR20 and including UHBR13.5.
See main article: Thunderbolt (interface).
The USB4 specification states that a design goal is to "Retain compatibility with existing ecosystem of USB and Thunderbolt products." Compatibility with Thunderbolt 3 is required for USB4 hubs; it is optional for USB4 hosts and USB4 peripheral devices.[28] Compatible products need to implement 40 Gbit/s mode, at least 15 W of supplied power, and the different clock; implementers need to sign the license agreement and register a Vendor ID with Intel.[29]
During CES 2020, USB-IF and Intel stated their intention to allow USB4 products that support all the optional functionality as Thunderbolt 4 products. The first products compatible with USB4 were Intel's Tiger Lake processors, with more devices appearing around the end of 2020.[30] [31]
Thunderbolt 4 is an implementation of USB4 "40 Gbps". It mandates some features that are optional in USB4 and mandates minimum PCIe ("32 Gbps") and DP capabilities (2 DP tunnels, "4K60 each", HBR3+DSC).[32]
Thunderbolt 5 is an implementation of USB4 "80 Gbps". It mandates even higher minimum PCIe ("64 Gbps") and DP capabilities (2 DP tunnels, "6K60 each", unclear min. DP speed). It also mandates support for asymmetric 120 / 40 Gbit/s connections from hosts to docks but does not mention the reverse.[33]
USB4 has 24 pins in a symmetrical USB type C shell. USB4 has 12 A pins on the top and 12 B pins on the bottom.[34]
USB4 has two lanes of differential SuperSpeed pairs. Lane one uses TX1+, TX1−, RX1+, RX1− and lane two uses TX2+, TX2−, RX2+, RX2−. USB4 transfers signals at 20 Gbit/s per lane. USB4 also keeps the differential D+ and D− for USB 2.0 transfer.[35]
The CC configuration channels have the roles of creating a relationship between attached ports, detecting plug orientation due to the reversible USB type C shell, discovering the VBUS power supply pins, determining the lane ordering of the SuperSpeed lanes, and finally the USB protocol makes the CC configuration channel responsible for entering USB4 operation.[36]
| Name | Description | ||
|---|---|---|---|
| A1 | GND | Ground return | |
| A2 | SSTXp1 ("TX1+") | SuperSpeed differential pair #1, TX, positive | |
| A3 | SSTXn1 ("TX1-") | SuperSpeed differential pair #1, TX, negative | |
| A4 | VBUS | Bus power | |
| A5 | CC1 | Configuration channel | |
| A6 | Dp1 | USB 2.0 differential pair, position 1, positive | |
| A7 | Dn1 | USB 2.0 differential pair, position 1, negative | |
| A8 | SBU1 | Sideband use (SBU) | |
| A9 | VBUS | Bus power | |
| A10 | SSRXn2 ("RX2-") | SuperSpeed differential pair #4, RX, negative | |
| A11 | SSRXp2 ("RX2+") | SuperSpeed differential pair #4, RX, positive | |
| A12 | GND | Ground return |
| Name | Description | ||
|---|---|---|---|
| B12 | GND | Ground return | |
| B11 | SSRXp1 | SuperSpeed differential pair #2, RX, positive | |
| B10 | SSRXn1 | SuperSpeed differential pair #2, RX, negative | |
| B9 | VBUS | Bus power | |
| B8 | SBU2 | Sideband use (SBU) | |
| B7 | Dn2 | USB 2.0 differential pair, position 2, negative | |
| B6 | Dp2 | USB 2.0 differential pair, position 2, positive | |
| B5 | CC2 | Configuration channel | |
| B4 | VBUS | Bus power | |
| B3 | SSTXn2 | SuperSpeed differential pair #3, TX, negative | |
| B2 | SSTXp2 | SuperSpeed differential pair #3, TX, positive | |
| B1 | GND | Ground return |
USB4 is supported by:
Brad Saunders, CEO of the USB Promoter Group, anticipates that most PCs with USB4 will support Thunderbolt 3, but for phones the manufacturers are less likely to implement Thunderbolt 3 support.[6]
On 3 March 2020, Cypress Semiconductor announced new Type-C power (PD) controllers supporting USB4, CCG6DF as dual port and CCG6SF as single-port.[41]
In November 2020, Apple unveiled MacBook Air (M1, 2020), MacBook Pro (13-inch, M1, 2020), and Mac mini (M1, 2020) featuring two USB4 ports.
AMD also stated that Zen 3+ (Rembrandt) processors will support USB4[42] and released products do have this feature after a chipset driver update.[43] However, AMD has only announced support for USB 3.2 Gen 2x2 in Zen 4 processors that were released in September 2022.[44] [45] Intel supports Thunderbolt 3 and USB-C with the mobile 9th generation processors in 2019.