---
id: external-drives.what-is-bus-power
url: https://storagestudio.us/faq/external-drives/what-is-bus-power
category: "External drives"
subcategory: "Speed, cables and hardware"
question: "What does bus-powered mean, and why won't my drive work on some ports?"
alt_questions:
  - "Bus powered external drive not enough power"
  - "Does my hard drive need a power adapter?"
  - "External drive works on one port but not another"
  - "USB hub not enough power for drive"
  - "portable drive powered by usb cable"
short_answer: "A bus-powered drive gets its power through the cable. Ports — and especially unpowered hubs — can only supply so much, so some drives fail or disconnect on weak ports. Plug directly into the Mac or use a powered hub; desktop drives need their own adapter."
tags: ["bus power", "usb", "hub", "power"]
related: ["https://storagestudio.us/faq/external-drives/should-i-plug-the-drive-into-a-hub-or-directly", "https://storagestudio.us/faq/external-drives/my-external-drive-keeps-disconnecting", "https://storagestudio.us/faq/external-drives/does-it-matter-which-port-i-use"]
applies_to: "all"
last_reviewed: 2026-10-01
---

# What does bus-powered mean, and why won't my drive work on some ports?

A **bus-powered** drive takes its power from the cable instead of a power adapter. Most portable SSDs and small portable hard disks work this way. Each port can supply only so much power, and hubs share theirs between everything plugged in, so a hungry drive can fail to start, disconnect, or click on a weak port.

What helps:

- Plug the drive directly into the Mac, not into an unpowered hub or a keyboard port.
- Use a hub or dock with its own power supply.
- Larger desktop hard disks always need their own power adapter — use it.

If a drive only misbehaves on certain ports, power is the likely cause. See [whether to use a hub or plug in directly](https://storagestudio.us/faq/external-drives/should-i-plug-the-drive-into-a-hub-or-directly).