When using Daemon Tools, what's the difference between...?

[ReyeZ]

When using Daemon Tools, what's the difference between a DT Virtual Device and an SCSI Virtual Device? And what the heck do they stand for? I remember the good old days when it was just simply a virtual CD or DVD. Apparently, I've been out of the loop when it comes to ISO files.

I've been using my own program that I made that simulates the CD/DVD bit for bit and it has never failed me. I never understood the need for emulation if you just copy everything, including the sectors that are suppose to be bad sectors or non written sectors. But living with the times, I gotta start using ISO files. Can anyone help with the lingo? -Thanks

[Terramex]

SCSI devices provide advanced emulation as required for most copy protections; e.g. those based on varying sector density (SecuROM, ProtectCD, Starforce, CD/DVD Cops).
They rely on the SCSI Pass Through Direct (SPTD) access layer driver.
Mainly as some security software makers are not willing to adjust their products to not conflict with SPTD, Disc Soft introduced the simple DT devices which don't provide advanced emulation,
and don't need the SPTD layer to be installed.