Secure erase story

Here's the thing.

I am trying to clean up my iMac 7,1 so that i can pass it on to my son.

I found a file called "Previous Systems" which occupied about 197GB of the HD. So I "secure erased" it. It showed over 500,000 files it was deleting! After 60 hours (yes, 60 hours) it finally finished.

It made NOT ONE MB of difference to the HD free space!

So, riddle me this Macman. What was my computer doing for two and a half days? (If it had pants and a pocket, I could guess!)