RIM is reportedly taking a $ 485 million charge to write off the value of its BlackBerry PlayBook tablet inventory. With the device slashed to a fraction of its original price and still not moving, RIM may soon follow in HP’s footsteps and kill the PlayBook entirely.

I don’t really know how all that fancy business accounting magic works, but using simple math based on the full $ 500 retail price of the base 16GB PlayBook, it seems like RIM is sitting on–and writing off 970,000 or so units. That’s a lot of unsold tablets.