Q:

Creation of 1.3 GB file takes only 1 second. How?

I have folder which contains over 200 files and has size of over 1.3 GB:

I use Gizmo Drive software to create an .iso file from that folder.

The interesting thing is it takes only 1 or 2 seconds!

I have tried that several times. I even tried to create the .iso file on another volume. Again it takes only 1 or 2 seconds. 
I tried to mount the .iso file, everything works fine. I thought that it might be an .iso file referencing the source folder then I moved the source folder to another place but no luck. Even copying the produced .iso file takes minutes!
So how come creating the .iso file takes only 1 second!
Do you have any explanation for that?
Notes

All tests conducted on a regular HDD, no SSD.
Using Windows 7 x64, have 16 Gig memory, Core i5 CPU.

I have used sync.exe to flush all file system data to disk just after the .iso file is created and sync.exe took 14 seconds to flush the data. That means it actually takes 14 seconds to create the .iso file. A quick benchmark on my D: drive shows that it can write the same .iso file from an SSD to my D: drive in 14 seconds and that confirms the source folder is in RAM and it takes 14 seconds to flush the data.**

A:

With 16GB of RAM, you probably have a lot of it free for disk caching.  The ISO has most likely just been buffered entirely in RAM by the operating system; it'll be written to disk later, but applications don't have to wait for that.

