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?

marked as duplicate by Karan, Scott, Tog, davidgo, Dave M Apr 12 '13 at 21:33

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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 falt 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?


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:

enter image description here

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.

  • One good example that it is not hardware enforced is the Canon alternative firmware CHDK that only runs when the SD card is locked. Since it also needs to save the photos you've taken to the very same locked SD card, it must ignore the setting to do so. – Richard Apr 12 '13 at 11:43

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

  • Sorry, -1, there simply is no "write" pin on an SD card. There are 4 data pins (both read and write), one command/response pin (needed for all commands), 2 GND pins, one clock and one power. Disconnecting any would break read functionality. – MSalters Apr 12 '13 at 11:13
  • This is wrong, see my comment about CHDK. If the pin was physically broken, the way CHDK is currently implemented would mean you'd have no way to save your photos - so rendering it useless. – Richard Apr 12 '13 at 11:45
  • @MSalters Those are the the SD Card pins, not the memory pins. The chip inside the card has tens of pins, one of them will switch the write protection. It is a hardware feature. – Havenard Apr 12 '13 at 23:35
  • @Havenard: do you have a reference for this? – intuited Oct 16 '14 at 22:42
  • If you open a SD Card with this switch you will see the switch simply cuts one of the chip's pins, just like an EEPROM. If that pin isn't energized it won't let you overwrite the chip. Its that simple. I don't have any online reference, just real life one. – Havenard Oct 16 '14 at 23:26

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