The short answer
Hold Option and choose Apple menu → System Information, select USB in the sidebar and click the device. The speed line shows the speed the connection negotiated: Link Speed: 480 Mb/s on macOS 27, Speed: Up to 480 Mb/s on earlier versions. 480 Mb/s is USB 2. If the drive supports 5 or 10 Gb/s, something between it and the Mac is limiting it, usually a charging cable, a USB 2 cable or a hub. Thunderbolt and USB4 devices are listed under Thunderbolt/USB4 instead. Connect the drive straight to the Mac with a cable rated for its speed, then check the line again.
On this page
Open System Information
- Hold the Option key and choose Apple menu → System Information. Or choose Apple menu → System Settings, click General, then About, then System Report.
- In the sidebar, under Hardware, select USB.
- Click the device in the list. Its details appear below.
Devices are listed under the bus and the hub they connect through, so a drive on a hub appears under that hub. The window doesn't update by itself. After you replug something, choose File → Refresh Information.
Read the speed line
On macOS 27 the line is Link Speed, for example Link Speed: 480 Mb/s. Earlier versions of macOS show the same figure as Speed: Up to 480 Mb/s. Both mean the same thing: the speed this connection negotiated when the device was plugged in.
The line shows what the connection got. A 10 Gb/s SSD on a USB 2 cable reports 480 Mb/s. To know whether the figure is right, compare it with the speed on the drive's box or spec sheet.
| Speed line | What it is | Typical devices |
|---|---|---|
| 12 Mb/s or less | USB 1.1 | Many keyboards and mice |
| 480 Mb/s | USB 2 (Hi-Speed) | Webcams, printers, phones, and anything on a charging cable |
| 5 Gb/s | USB 3 (USB 3.2 Gen 1) | Hard drives, flash drives, many hubs |
| 10 Gb/s | USB 3 (USB 3.2 Gen 2) | Portable SSDs |
| 20 Gb/s | USB 3.2 Gen 2x2 or USB4 | Faster portable SSDs |
| 40 Gb/s | USB4, Thunderbolt 3 and Thunderbolt 4 | Thunderbolt SSDs, docks and displays |
12 Mb/s or less
- What it is
- USB 1.1
- Typical devices
- Many keyboards and mice
480 Mb/s
- What it is
- USB 2 (Hi-Speed)
- Typical devices
- Webcams, printers, phones, and anything on a charging cable
5 Gb/s
- What it is
- USB 3 (USB 3.2 Gen 1)
- Typical devices
- Hard drives, flash drives, many hubs
10 Gb/s
- What it is
- USB 3 (USB 3.2 Gen 2)
- Typical devices
- Portable SSDs
20 Gb/s
- What it is
- USB 3.2 Gen 2x2 or USB4
- Typical devices
- Faster portable SSDs
40 Gb/s
- What it is
- USB4, Thunderbolt 3 and Thunderbolt 4
- Typical devices
- Thunderbolt SSDs, docks and displays
480 Mb/s isn't a fault by itself. Keyboards, mice, printers and many webcams only support USB 2 or slower, and they don't need more. It's a problem when the device supports more: an external SSD, a fast flash drive, a dock or a card reader.
Thunderbolt and USB4 devices
Thunderbolt and USB4 devices have their own list. In the sidebar, select Thunderbolt/USB4. Each of the Mac's ports is listed as a bus, with a Status line and a Speed line such as Speed: Up to 40 Gb/s.
Status: No device connectedmeans the port is empty. The Speed line is then what the port can do.- A connected Thunderbolt or USB4 device appears under its bus by name, with a Status and a Speed line for the port it's connected through.
- A USB 3 drive plugged into a Thunderbolt port isn't a Thunderbolt device. It appears under USB, not here.
So if a Thunderbolt drive shows up under USB, it has connected as a plain USB device. Check the cable first.
The same check in Terminal
system_profiler SPUSBDataType SPUSBHostDataTypesystem_profiler SPThunderboltDataTypeLook for the Link Speed line under each device, or Speed on earlier versions.
Why a fast drive connects at USB 2 speed
A connection runs at the fastest speed that every part of the chain supports: the Mac's port, the cable, any hub or dock in between, and the device. The slowest part sets the speed.
The cable
USB-C is the shape of the plug, not a speed. Two USB-C cables can look the same and carry very different speeds. Cables made for charging often have only the USB 2 data wires, so anything connected through them stops at 480 Mb/s, whatever the drive and the Mac can do.
Apple's own USB-C Charge Cable is one of them. Apple says its data transfer is limited to 480 Mbps (USB 2.0) and that it doesn't carry video. The cable that came with a charger or a phone is often this kind. The short cable that came with the SSD is the one made for it.
A hub or dock
Everything on a hub shares the hub's one connection to the Mac. A USB 2 hub, or a USB 2 port on a mixed hub, limits the device on it to 480 Mb/s. The hub's own cable counts too. The USB ports on some displays and keyboards are USB 2 hubs.
The port or the device
Some devices only support USB 2, and no cable makes them faster. A plug that isn't pushed all the way in can also connect at USB 2 speed, so reseat it before you blame the cable.
What USB 2 speed costs you
At 480 Mb/s the link carries at most 60 MB a second, so a 50 GB folder takes at least 14 minutes. A 10 Gb/s link can carry about 20 times more, and the drive becomes the limit instead of the cable.
Find what's limiting it
- Connect the drive straight to a port on the Mac, with no hub, dock or display in between. Refresh System Information and read the speed line.
- If it still says 480 Mb/s, change the cable. Use the one that came with the drive, or one marked with a speed such as 10 Gb/s or 40 Gb/s. A Thunderbolt cable has the Thunderbolt logo on each connector.
- If the speed is right when connected directly, the hub or dock was the limit. Move the drive to a faster port on it, or keep the drive on the Mac and put slower devices on the hub.
- Try another port on the Mac, and push the plug fully in.
- If nothing changes, check the drive's own spec. It may be a USB 2 or 5 Gb/s device.
Cables limit charging too
The same goes for power. In System Information, select Power and find AC Charger Information. Wattage (W) is what the Mac and the charger agreed on.
If it's lower than the charger's rating, the cable is one possible cause. In USB Power Delivery, charging at 100 W needs a cable rated for 5 A, and the levels from 140 W to 240 W need a cable built for 240 W.
The faster way: the slow cable check in iKnowMyMac
System Information shows the speed when you go and look, and leaves the comparison to you. iKnowMyMac's Connected list shows each device's speed next to what it supports, so a drive running at 480 Mb/s of 10 Gb/s stands out without a spec sheet. When a cable or hub holds a drive back, you get a heads-up. It also shows what a charger supplies.
USB Log
Every device that connected to this Mac · kept on this Mac
USB Keyboard · if it isn't yours, unplug it
With it: the USB log
- USB log. Every USB and Thunderbolt device that connects to your Mac, with time, name and what it is, including while the Mac is locked or at the login window.
- New keyboard alert. An urgent alert the moment a keyboard your Mac hasn't seen before connects.
- Safe look. A read-only overview of an unknown drive's files before you open anything from it.
- It stays on your Mac. The USB log records device names and IDs, never file contents.
Sources
- 1.System Information User Guide for Mac (Apple)
- 2.About the Apple Thunderbolt 3 (USB-C) Cable, and how it differs from the USB-C Charge Cable (Apple)
- 3.Identify the ports on your Mac (Apple)
- 4.USB Data Performance Language Usage Guidelines (USB-IF)
- 5.USB 3.2 Specification Language Usage Guidelines (USB-IF)
- 6.USB Charger: USB Power Delivery (USB-IF)