TC FTP plugin on Android. Question about how works 'copy to buffer'

[singlequestion]

When i'm connected to my PC's ftp via TC FTP plugin. And when i marked files that i want to download to my Android. And when i choosed 'copy to buffer' in popup menu.

what is the buffer?
Is it Android flash memory? or Android RAM?

And what i'm copyed?
URL's on files, or full files. I assume file can be big, so it's just url's =)

I'm just care that when i choose 'copy to buffer' and than 'paste here'(on my SD card dir) i'm not use constant flash memory of my smartphone.

In other words i want to be sure that download process looks like files transfer directly from FTP server to SD card. Without using
flash memory of my android device.