External drives · Speed, cables and hardware
Why does it take a few seconds to open something from my external hard disk?
Short answer: Hard disks spin down when idle and take a few seconds to spin up again on first access. SSDs don't. You can change macOS's hard-disk sleep setting in System Settings, or use an SSD for frequently opened items.
A spinning hard disk powers down its motor when idle, and spinning back up takes a few seconds the first time something asks for a file. That's normal for hard disks and doesn't happen with SSDs.
If the delay bothers you, you can turn off Put hard disks to sleep when possible in System Settings (under Energy or Battery options, depending on your Mac), at the cost of a little more power use. For apps and folders you open often, an SSD avoids the delay entirely.