I think it is the ATA Security Erase I wrote about. Tough it seems it may
refer to different ways of doing the erase.
Not sure how this works but I used Secure-erase-enhance option. It trashed my HDD for 133min. So I am guessing this completely overwrote the drive. This is the best option I have used so far.
usually OS dependent. like dd, shred. dban, all have a significant overhead as they have to use the OS resources and other components of the pc.
With Security Erase, there was no stress on the system. the whole operation was limited to the HDD. I was able to continue using the system.
using DD, the cpu was always over 60% all the time.
Given from the time difference, I think, that the Intel SSD 320 security
erases itself by deleting the crypto key, and that your harddisk might do
it by overwriting its data. Cause when your harddisk used encryption and
just overwrote the crypto key, then it should be able to security erase
quicker than in 132 minutes. And if the Intel SSD overwrote all of its
data to security erase itself it would need longer.
Not sure how SSDs work, never used one.