I just bought a new mac and need to clear the memory of my old one but i don't have a startup disk. how do i do this?

Question

I just bought a new mac book pro and need to clear my old mac of it's contents to give it away---  I do not have my startup disk anymore.  How can i completely delete my old mac's memory?

Answer 1

Erasing your drive:
Dragging the files to the Trash removes the references to them from the Directory. As has always been the tradition, the data blocks that held the actual data are not over-written, they are merely added to the free list for later re-use. Their original contents are still present.
Disk Utility "Erase" or "Partition" of a drive (which finishes in under a minute) also does not over-write the data blocks, but merely creates a new, empty directory.
To clear the data that may still be present (admittedly in a disorganized mess of unlinked blocks) you need to overwrite the data. Use the erase tab, then choose "Security Erase" Options, and overwrite once with Zeroes. This process can take several hours as it is -- if you insist on multiple passes, it can take days to complete, with little additional protection. Multiple passes is unnecessary unless your drive held Military Secrets.
When you have erased, be sure to install some version of Mac OS X -- a Mac with no obvious Operating software may be dead, and  is much more likely to quickly become landfill.