Same plug. What’s inside?
Open a cable. Explore its parts. See what changes when you switch.
Three example cables · See what the wires do, what changes between cables and how that affects charging, file transfers and screens. The exact construction varies by manufacturer.
Loading the 3D cable… Component descriptions are available below.
Select a component to trace its role.
- Data
- 40 Gbps in TB4 operation
- Power
- Up to 100 W
- Video
- Supports video
Where does the wire connect?
These are enlarged views looking straight into the open end of each cable plug, with its cable pointing away from you. A and B name the two rows of metal contacts; the numbers identify their positions.
Choose a wire to see the contacts it joins highlighted in blue.
No wire selected
No wire selected
Blue + dot: selected connection · Gold: other contacts · Gaps: no contact in this example.
Technical detail: reading the plug views
Both drawings use the same fixed front-view orientation, independent of the 3D camera. Top row: A12 to A1 from left to right. Bottom row: B1 to B12. These are cable plugs, not the sockets on your devices. B6 and B7 are absent. In the Thunderbolt examples, B5 supplies the local e-marker through VCONN rather than running to the other plug. The basic example shows only its connected contacts.
More room for your screens.
2 lanes each way
Information can travel both ways at once, with 80 Gbps of capacity in each direction.
Think of the four wire pairs as four lanes for information. These buttons show how they can be shared between directions. Your connected devices choose the real mode automatically; the wires stay the same.
What the Thunderbolt examples add
Orange identifies parts added to the basic USB 2.0 example; shared parts stay in place. Electric blue identifies your selection. Switch between cables to compare the same view.
- Basic USB-C
- Everyday USB 2.0 data · up to 60 W · no direct video
- Thunderbolt 4 reference
- Four fast data pairs · 40 Gbps with TB4 devices · up to 100 W in this example
- Thunderbolt 5 reference
- The same four pairs · 80 Gbps each way or 120/40 Gbps · up to 240 W in this example
Both Thunderbolt examples have the same number of fast data wires. Thunderbolt 5 uses them to carry more information. Orange marks additions compared with the basic cable, not differences between TB4 and TB5.
The Thunderbolt examples also have an identity chip, its power supply and a small power-smoothing component. Other USB-C cables can have these too. A cable that carries more charging power is not necessarily faster at transferring files.
Inside the Thunderbolt 4 example
This example adds four pairs of fast data wires, extra control wires and an identity chip in each plug. It supports data and video at up to 40 Gbps in a Thunderbolt 4 connection. It is a passive cable: it has no electronics that boost or rebuild the data signals. Compatible passive cables can also carry faster Thunderbolt 5 signals when the devices at both ends support them.
The blue pairs, purple sideband paths and identity chip are additions to this particular basic USB 2.0 example. E-markers are also used in other USB-C cables. Shielding and other construction details can also differ.
A cable’s label is not always its physical limit
A Thunderbolt 4 connection runs at up to 40 Gbps. Some compatible passive cables sold for that speed can also carry faster Thunderbolt 5 signals. Both connected devices must support the faster connection. Passive means the cable has no electronics that boost or rebuild the data signals; active cables do, so the same rule does not apply to every cable.
So a cable’s chip may report an older 40 Gbps rating while your Mac reports an 80 Gbps connection. That alone does not mean the cable’s label is false. Intel explains compatibility with existing passive cables in its Thunderbolt 5 technical brief.
A cable is one part of the connection
Want to check your own setup? See what the free app tells you, or explore WhatCable Pro’s deeper charging and display checks.
WhatCable checks what your Mac can tell it about the port, cable and device or charger at the other end. It compares what each can support with the connection they are actually using. If you have a dock, it uses the available information to separate the Mac-to-dock connection from the accessories plugged into it.
For example: an 80 Gbps port connected to a Thunderbolt 4 device is limited to 40 Gbps by that device, even if the passive cable can carry faster signalling. Replacing only the cable will not make that device run faster. WhatCable’s diagnostic accounts for that rather than blaming the cable.
For displays: WhatCable Pro’s Display Diagnostics checks how much detail your screen shows, how often the picture updates and what the display connection can carry. It also accounts for picture compression and adapters when that information is available. That helps explain why a screen is not running as sharply or smoothly as expected.
What do the numbers mean?
Mbps and Gbps describe data capacity. One Gbps is 1,000 Mbps. More capacity can help with large files and demanding screens, but the devices at both ends matter too. File-copy speeds are often shown in megabytes per second (MB/s), a different unit, and will also be affected by the work needed to organise the transfer.
Watts (W) describe power. A 240 W cable can carry more charging power than a 60 W cable, but your charger must supply it and your device must support it. More watts do not mean faster file transfers.
Follow the connections
The metal contacts inside a plug are the points where its wires connect to a device. This table follows each connection from the plug shown in 3D to the plug at the other end. A and B name the two rows of contacts. TX means transmit; RX means receive. These labels name the contacts, not a fixed direction for every connection mode.
| Signal | Plug 1 | Plug 2 |
|---|---|---|
| Ground bus | A1, A12, B1, B12 | A1, A12, B1, B12 |
| VBUS bus | A4, A9, B4, B9 | A4, A9, B4, B9 |
| CC | A5 | A5 |
| D+ | A6 | A6 |
| D− | A7 | A7 |
| TX1+ → RX1+ | A2 | B11 |
| TX1− → RX1− | A3 | B10 |
| RX1+ ← TX1+ | B11 | A2 |
| RX1− ← TX1− | B10 | A3 |
| TX2+ → RX2+ | B2 | A11 |
| TX2− → RX2− | B3 | A10 |
| RX2+ ← TX2+ | A11 | B2 |
| RX2− ← TX2− | A10 | B3 |
| SBU1 → SBU2 | A8 | B8 |
| SBU2 → SBU1 | B8 | A8 |
| Outer shield | Shell + ground | Shell + ground |
| Coaxial shields | Ground bus | Ground bus |
| VCONN (local) | B5 → local e-marker / Ra | B5 → local e-marker / Ra |
Technical notes about this model
Base wiring reference: USB-C Release 2.0, Tables 3-10 / 3-11 and Figure 4-42. The Thunderbolt 5 example extends this with PAM-3 signalling and EPR power requirements. The full-featured plug has 22 contacts; B6 and B7 are absent. The USB 2.0 example includes only its connected contacts. The cable uses coaxial shielding rather than separate drain wires. Opening the view separates layers and routes for inspection. Colours identify functions; distances, component blocks and PCB trace positions are not manufacturing dimensions. Power ratings require a compatible charger and device. Wiring alone does not establish Thunderbolt certification or signal-integrity compliance.
Read the component guide without 3D
Outer cover · jacket
The flexible outer cover protects the wires from everyday wear and keeps the cable together. Manufacturers use different materials and thicknesses for this cover, also called the jacket. A thicker cable is not automatically faster.
§3.4 · Table 3-10 notes · cable shielding
WhatCable checks reported capabilities and connection behaviour; it cannot inspect the physical wiring inside the cable.
Protection from interference
A layer of metal foil or woven wire helps keep unwanted electrical noise away from the signals inside. This layer is called shielding. It surrounds the wires and connects to the metal shell of each plug. The shell is also connected to ground, the circuit’s common reference. In this model, each fast data wire has its own shield too.
§3.4 · Table 3-10 notes · cable shielding
How WhatCable helps: WhatCable watches the error counts reported by your Mac’s port. Changes can help you spot a recurring connection problem.
An error count does not identify a damaged shield. Repeated connection events can also come from movement or unplugging. WhatCable highlights the pattern so you can investigate.
Charging wires · VBUS
These wires carry the electricity that charges your laptop, phone or other device. The technical name for this power connection is VBUS. With USB Power Delivery, the charger and device agree how much power the connection can provide, taking the cable’s rating into account. They exchange those messages over the separate CC control wire. The red route groups the power wiring together; it does not show an exact wire count.
Tables 3-10 / 3-11 · plug-to-plug wiring
How WhatCable helps: Slow charging does not always mean the cable is at fault. WhatCable compares what the charger can supply, what the cable is rated to carry and the charging power your Mac and charger have agreed to use. It also checks whether the battery is full or charging is on hold.
The agreed power is a limit, not a measurement of what the Mac is using every moment. WhatCable can also identify a second charger on standby.
Return wires · ground
These wires complete the electrical circuit, giving the charging current a path back to its source. Ground, labelled GND, also gives the electronics a common voltage reference. Several metal contacts in the plug share this connection, so the number of contacts is not the number of separate wires.
Tables 3-10 / 3-11 · plug-to-plug wiring
Everyday data · USB 2.0
Two wires carry data for USB 2.0 devices. They can transfer files, but are much slower than the extra data wires in a Thunderbolt connection. The wires are labelled D+ and D−. They work as a pair and support signalling up to 480 Mbps. Both Thunderbolt examples retain them for USB 2.0 devices; faster traffic uses separate pairs.
Tables 3-10 / 3-11 · plug-to-plug wiring
How WhatCable helps: A mouse plugged into a fast dock does not need a fast connection. WhatCable separates the Mac-to-dock connection from the devices attached to the dock, so a slower accessory is not automatically treated as evidence of a slow cable.
Connection setup · CC
This control wire helps the devices recognise the connection and agree how charging should work. It also lets them talk to the cable’s identity chip, when one is fitted. CC means Configuration Channel. It carries setup and power messages, not your files. The USB-C connection uses it to detect attachment and plug orientation, negotiate USB Power Delivery and read cable identity.
Tables 3-10 / 3-11 · plug-to-plug wiring
How WhatCable helps: WhatCable brings together information about the cable, the device at the other end and the connection they have made. This helps explain what is limiting the connection.
It also checks that the connection is still active, so old charging information left behind after unplugging is not mistaken for a current connection.
Fast data & video wires
Eight wires, working in four pairs, carry fast data and video. These are the extra paths missing from our basic USB 2.0 cable. Each pair carries one signal using the difference between its two wires; this is called differential signalling. Each wire has its own surrounding shield in this model. TX and RX in the table mean transmit and receive. They name the contacts, while the connection mode determines how the paths are used. Compatible passive cables can carry newer PAM-3 signalling with faster devices; that does not make a Thunderbolt 4 port faster.
Tables 3-10 / 3-11 · plug-to-plug wiring
How WhatCable helps: WhatCable checks the Mac’s port, cable and connected device together to help explain a slow connection. If you use a dock or a chain of Thunderbolt devices, it uses the connection information your Mac provides to work out where a limit may come from.
When enough information is available, it follows a Thunderbolt chain with no branches through to its last device. It can also identify when macOS is blocking an accessory. For screens, WhatCable Pro’s Display Diagnostics checks picture resolution, refresh rate (how often the picture updates) and the capacity of the display connection. It accounts for Display Stream Compression, or DSC, which lets a picture fit into less connection bandwidth. If macOS does not expose enough information, WhatCable does not guess.
Extra control wires · SBU
These two wires carry small control messages for certain connection types. For example, they help a DisplayPort connection manage the screen; the picture itself uses the fast data wires. SBU means Sideband Use. What these wires do depends on the connection mode. DisplayPort Alt Mode, which carries DisplayPort through USB-C, uses them for its AUX (auxiliary) control channel.
Tables 3-10 / 3-11 · plug-to-plug wiring
How WhatCable helps: Screen not as sharp or smooth as expected? WhatCable Pro checks its resolution, how often the picture updates and the display connection. It also uses adapter information when available, including USB-C-to-HDMI connections.
The display connection may run at a lower speed because that is enough for the picture setting you chose. Choosing a more demanding setting may cause it to use a faster connection. WhatCable reads the reported settings; it does not electrically test these individual wires.
E-marker · cable identity
A tiny chip inside the plug acts like the cable’s digital label. It tells connected devices what the cable says it can support, including its data and charging capabilities. This chip is called an e-marker. Our example has one in each plug. It talks over the CC control connection, gets power through VCONN and connects to ground. A resistor called Ra tells the connected device that the chip needs power. Full-featured cables require e-markers, as do USB 2.0 cables carrying more than 3 A of current. Having an identity chip does not make a cable “active”: that term refers to electronics that process its data signals.
§4.9 · Figure 4-42 · e-marker at each end
How WhatCable helps: WhatCable compares the cable’s digital label with the connection your Mac reports. A difference is a reason to look closer, not automatic proof that the cable is faulty or falsely labelled.
For example, a compatible passive cable with an older 40 Gbps identity can work at 80 Gbps with newer signalling. A slower connection can instead be limited by the port or device. WhatCable Pro’s Negotiation Diagnostics shows the figures for each part of the connection. A missing manufacturer ID alone does not prove a cable is fake; WhatCable considers the other identity fields too.
Shields around the data wires
Each fast data wire has its own metal shield wrapped around it. This helps protect the signal from electrical noise. This arrangement is called coaxial construction: the signal wire runs through the centre of its shield. The shields connect to ground in both plugs. Other cables use shielded twisted pairs and separate drain wires to connect the shielding. Those are different construction choices; this model uses the coaxial option in USB-C Table 3-10.
§3.4 · Table 3-10 notes · cable shielding
Power for the chip · VCONN
The identity chip needs a little power of its own. This connection supplies it separately from the wires that charge your device. VCONN is the name for this chip supply. In our example, contact B5 powers the chip in its own plug; no VCONN wire runs all the way through the cable. Each chip also connects to CC and ground. A resistor called Ra between B5 and ground signals that chip power is needed.
§4.9 · Figure 4-42 · e-marker at each end
How WhatCable helps: If WhatCable cannot show the cable’s identity chip, try connecting a charger, dock or device at the far end. Some Macs wait for that connection before reading the chip. Missing information does not automatically mean the chip is absent or broken.
Power smoothing · capacitor
This small part briefly stores and releases electrical charge, helping smooth rapid changes on the power connection inside the plug. It is called a bypass capacitor. In our Thunderbolt 4 example, a 10 nF capacitor connects between VBUS (power) and ground in each plug, close to the power contacts. The unit nF describes how much charge a capacitor can store for a given voltage. The reference specifies at least a 30 V voltage rating. This example uses Standard Power Range (SPR), up to 100 W. The higher-voltage Thunderbolt 5 example needs a different voltage rating.
Tables 3-10 / 3-11 · plug-to-plug wiring
Thunderbolt 5: what changes
Thunderbolt 5 sends more information through the same four pairs of fast data wires. It can carry 80 Gbps each way, or give demanding screens more capacity in one direction. This example also supports charging up to 240 W, with suitable power components and an identity chip in each plug. These are example designs; manufacturers can build the inside differently.
Highspeed
Thunderbolt 5 carries more information through the same eight fast data wires. It uses three electrical signal levels instead of two; this is called PAM-3. The four wire pairs act as four data lanes. Normally, two lanes send and two receive, giving 80 Gbps each way. Bandwidth Boost changes that to three lanes towards demanding screens and one back: 120 Gbps one way and 40 Gbps the other. These are connection capacities, not promised file-copy speeds. The devices and the messages needed to organise transfers also affect performance.
Intel · Thunderbolt 5 signalling and bandwidth
Power
These wires can carry up to 240 W in this example, if both the charger and device support it. A higher cable rating does not make a device take more power than it needs. This uses Extended Power Range (EPR), the USB charging range above 100 W. It needs suitable insulation, plugs, components and an EPR-capable identity chip. The maximum charging contract is 48 V at 5 A: 240 W. Volts (V) describe voltage, amps (A) describe current, and watts (W) describe power. Thunderbolt 4 cables can also support EPR; 100 W is the rating chosen for our TB4 example, not a universal TB4 limit.
UL Solutions · 240 W EPR cable requirements
Marker
Each plug in this example has its own identity chip, powered through VCONN. The chip reports support for the cable’s data signalling and Extended Power Range (EPR) charging. That allows a suitable charger and device to agree up to 48 V at 5 A, or 240 W. The chip reports what the cable supports; it does not make the data signals faster.
UL Solutions · EPR cable marking
Capacitor
This small part helps smooth rapid changes on the power connection. Here it must also cope with the higher charging voltage used for up to 240 W. Our Thunderbolt 5 example uses a 10 nF bypass capacitor rated for at least 63 V. That higher voltage rating is needed for Extended Power Range charging. The 30 V minimum used for the older power range would not be enough. The capacitor connects between power and ground; charging current does not pass through it on its way to your device.
How to read this reference model
The electrical connections follow USB-C Release 2.0: §3.4 and Tables 3-10 / 3-11 define the cable wiring; §4.9 and Figure 4-42 describe the two-e-marker arrangement. Coaxial construction and that e-marker arrangement are permitted choices, not the only ways to build a cable. Colours, spacing and component blocks support inspection and are not manufacturing dimensions. Thunderbolt performance also requires its own compliance testing.
Thunderbolt 5 signalling follows Intel’s technology brief; its EPR power example uses the higher voltage and marking requirements described by UL Solutions. This does not mean every Thunderbolt 4 cable is certified for Thunderbolt 5. Each component’s expanded details link to the relevant specification section. The table above names both ends of each electrical connection.
Learn more: USB-IF cable specification · Intel’s Thunderbolt guide · Thunderbolt 5 technical brief · EPR cable requirements