|In addition to all the above sound advice you might think about what sort of information you write to your main hard drive on your new computer. |
If nothing of a sensitive nature is written to start, you don't need to worry about removing it when disposing of the computer.
That said, as XP User pointed out used computers are not worth much without an operating system and hopefully, some additional software.
I recently came across something about recycling centers selling hardware overseas. Hard drives were then scanned for information like credit card numbers that could be sold or used by the finder.
Many users don't even give a thought to the data on their computer.
There are multiple methods to keep sensitive data off the main drive.