SD card usage in multiple devices and formatting
 

I used my SD card in both my DSLR and my Camcorder. Therefore, I'm guessing that the SD card was reformatted to the last device that was in it. I have transferred the pictures from my SD to my PC. Subsequently, I deleted the pictures and videos on the SD card from my PC. When I placed the card back into the first device, it still showed the pictures on the SD card! And when I tried to take more pictures, the count on my DSLR was increasing, but I could new view the pictures on the camera. Do I need to reformat the SD on my camera to wipe out the original pictures that should have been deleted? Will the new pictures that I took then download onto the SD? This has happened to me before and I took out the SD card from my camera. Sadly, I lost approximately 300 pictures. This time, I don't want to take the SD card out for troubleshooting and risk losing approximately 160 pictures. HELP????

As a rule of thumb, a card only responds properly to the OS (operating system) of one device for which the card has been formatted (sometimes called "initalize").

Formatting (initializing) erases previous content, or at least the listing thereof, and frees up the memory space for data written to the card by the operating system of the device that did the formatting.

Above I said "responds properly" - there are times when you can get lucky - you take a card out of one device and insert it into another device, create data, and you end up with data from both still intact.

But more often than not something gets erased, or made unreadable, unless you strictly format ONE card to ONE device, and if you wish to use that card on another device, save the data before inserting and formatting the card in the "new" device.