How does sd card write lock work?

Question

Is this a software or hardware feature. If it is a hardware feature, what tells the os that it is "write protected"? If it is a software feature, is there anyway to override this? Also, is there any way to "write protect" another device such as a hdd or flash drive?

Answer 1

This is a software thing. You can enable the hardwarelock on your sd card and depending on the driver (software) you use it looks for the hardwarelook or not. Most software do it, because it is common sense to do so. But it does not mean that it really is protected against a program which really wants to write on your SD card.

Yes you can override this feature by software. I think there might be programs out there which can do this your do program one yourself on block level. (maybe lowlevel)

On other devices you might have a true hardware lock like this:

but must devices do not have such thing. Operating systems enable write protection with user rights or with filesystem rights.

You can also map an encrypted drive readonly via Truecrypt, which needs a password or password file. But this does not protect it from a person having the harddrive in her or his hands and format it.

Answer 2

It depends. We have had SD card readers that you could fool into believing an SD card was read-write by applying masking tape; we also had SD card readers that would flat out ignore the read-only switch.

SD card readers usually are USB. That means the OS will believe them, when they tell the OS a card is read-only. The OS won't allow write command to be sent. Software just can't ignore that.

That said, an SD card can physically implement its own read-only switch and ignore write commands. This isn't exceptionally hard, but would add about a dollar to the retail price.

See also Is the lock mechanism on an SD card hardware, firmware, or software (driver,OS) enforced?

Answer 3

Its a hardware feature. It physically disconnect a pin that would allow you to write to the memory.