So far, I watched this vid to about 8:30 - it was interesting. The guy mentions how Linux liveboot USBs store all files in RAM (if persistence is turned off); this is also true with Lubuntu, proof:
# RAM usage - baseline: 3,008,500,000 bytes free
lubuntu@lubuntu:~/Downloads$ free
total used free shared buff/cache available
Mem: 5552340 1018636 3008500 298968 1525204 3982676
Swap: 3300448 0 3300448
lubuntu@lubuntu:~/Downloads$ sudo dd if=/dev/random of=a bs=512 count=5000000
dd: warning: partial read (103 bytes); suggest iflag=fullblock
0+5000000 records in
0+5000000 records out
393122634 bytes (393 MB, 375 MiB) copied, 202.439 s, 1.9 MB/s
#
# RAM usage after creating a 393-megabyte file: 2,769,504,000 bytes free
lubuntu@lubuntu:~/Downloads$ free
total used free shared buff/cache available
Mem: 5552340 859520 2769504 672008 1923316 3768048
Swap: 3300448 0 3300448
lubuntu@lubuntu:~/Downloads$ sudo rm a
#
# RAM usage (baseline) after deleting said 393-megabyte file: 3,148,912,000 bytes free
lubuntu@lubuntu:~/Downloads$ free
total used free shared buff/cache available
Mem: 5552340 857144 3148912 288024 1546284 4154556
Swap: 3300448 0 3300448
lubuntu@lubuntu:~/Downloads$ sudo dd if=/dev/random of=a bs=512 count=9000000
dd: warning: partial read (115 bytes); suggest iflag=fullblock
0+9000000 records in
0+9000000 records out
710147097 bytes (710 MB, 677 MiB) copied, 342.028 s, 2.1 MB/s
#
# RAM usage after creating a 710-megabyte file: 2,575,796,000 bytes free
lubuntu@lubuntu:~/Downloads$ free
total used free shared buff/cache available
Mem: 5552340 748932 2575796 968492 2227612 3581916
Swap: 3300448 0 3300448
lubuntu@lubuntu:~/Downloads$ sudo rm a
#
# RAM usage (baseline) after deleting said 710-megabyte file: 3,168,480,000 bytes free
lubuntu@lubuntu:~/Downloads$ free
total used free shared buff/cache available
Mem: 5552340 825212 3168480 299816 1558648 4174820
Swap: 3300448 0 3300448
lubuntu@lubuntu:~/Downloads$ echo Free RAM space changes caused by creating and deleting a 100MB+ file.