I have an elderly Sony laptop and a more ancient desktop with unknown 
motherboard happily running i386 Debian 9.0. As far as I can tell the 
BIOS of neither machine supports booting from a flash drive. Neither 
has functional CD/DVD drive. Both hard drives have copious free space.
Both machines have internet access.
Though this machine is 64Bit capable and bootable from flash, it does 
not have adequate free space for an additional OS.
Are there documented install instructions covering machines described 
in first paragraph?
TIA