Is there a way to make a thumb drive read only?

Um. That’s pretty much it.

(I want to transfer some files via thumb drive and don’t want them accidentally overwritten.)

It should be possible. See here.

You used to be able to buy thumb drives with a small switch that would prevent writing on the drive. Many (all?) SD cards have that switch, so if you have a card reader in your computer you could use one of those.

All my thumb drives have a lock switch, but you have to look for it.

If you do not have a switch, you can flag files as Read-Only in Explorer/Finder.


The switch doesn’t really do anything but tell the computer not to write on it. I think the only methods available are through software.

Hmm maybe if you made the thumb drive appear as a CD? That way the computer wouldn’t attempt to write to it. But that would make it harder to use.

Are you sure? It’s a physical switch connected to the controller circuitry in the device - although I’m sure it would be possible to implement this so that it merely informed the host that the device is non-writable, it must also be quite easy to implement in a way where the controller just refuses to accept any write instructions (and that seems more sensible, as it would work independently of the reliability of the host).

I haven’t taken one apart, but I remember hearing you could fix (SD or Memory Stick) write protect switches with cellophane tape, just like the switches on VHS/cassette tapes.
Might have the answer.

On further investigation, it appears that the switch on USB thumb drives is generally implemented in hardware (so you can’t force an overwrite, no matter), whereas for SD cards, it’s a flag to the driver/OS to request that the volume be treated as read only, so in theory, it could be circumvented, although I guess that would mean writing/using a custom driver or something.

Or you could break off the sensing tabs in the card reader.

I’ve never heard of any switches on memory actually being electrically connected though. Which thumb drives have those?

Not many these days, but any USB thumb drive that has a switch will have it implemented in hardware (reason being: with SD cards, the ‘switch’ actually goes inside the reader, where a sensor can see it. With USB devices, they just plug into a standard USB port, which is not equipped to do anything other than connect the terminals - the switch stays outside on the device).

Here’s an example of the internals of a US drive with a write protect switch:

Some USB Flash Drives have hardware Read-Only switches - here is a list of some that are available in the US, and it looks pretty current.

It also appears that manufacturers are not producing as many USB drives with this functionality.


Well, I’ve just inspected the eight thumbdrives I have on hand, and none of them have any sort of physical switch visible.

So off to buy another. Thanks for the list, Si!

It’s possible that some of your devices have PCB tracks for a switch, but no switch. If any of them happen to be easy to pop open, it might be worth a look inside.