Why is a DFU restore install so quick?

[UndercoverCroc]

Have recently been wondering, when an SSD is wiped, installing MacOS using internet recovery seems to take up to a couple of hours regardless of download speeds.

However, linking up another mac and DFU restoring a new version of MacOS, presumably the exact same package, is so much quicker, 12 mins or so- why?

 

[Fishrrman]

This is an entirely uneducated GUESS on my part.

When you do the DFU restore...
- it takes only as long to download the DFU "installer" as your internet connection will support (that is, even a 12gb file may download in a few minutes)...

then...
- The DFU "installer files" might themselves are "pre-configured images" that can be written "en masse" to the target Mac's drive.
That means that all Apple Configurator does is "set up" the internal drive with pre-configured partitions/containers, and then "pours" a single, giant install file into each one, instead of writing tens of thousands of "individual files".

- The high speed of the internal drives (particular on MacBook Pros) makes the "copying process" go quickly.

- Some final configuration and "touch ups", and the install is done.

Or... to put it another way...
There's less "installing", and a good deal more "[only] copying".

Again, this is a complete GUESS and I could be totally wrong.
I welcome correction from those "in the know".