Hi,
If you only plugged in a single hard disk, then it will be called sda. The second one would be called sdb, next one sdc, etc. I believe Frank just wanted to make sure. If you want to check, you can list the devices whose name starts with sd, like this (the * is a wildcard, so the command will list sda, sdb, sdc...):
ls /dev/sd* -l
Your output should look something like this:
brw-rw---- 1 root disk 8, 0 Feb 22 07:40 /dev/sda
brw-rw---- 1 root disk 8, 1 Feb 22 07:40 /dev/sda1
Not identical, but look at the end of the first line.
There is a good chance that the file
/etc/udev/rules.d/50-hdparm.rules does not exist, until you make one. Frank is suggesting using the "nano" text editor to do that. So this command below will open a blank file, in the nano editor, with that exact name:
nano /etc/udev/rules.d/50-hdparm.rules
Frank is giving you something to copy and paste into that file, that will change the behavior of the disk drive. After you paste it into the empty file, <ctrl><x>, and then <y>, will exit the editor, and save the file.
The rest, I am afraid, is above my paygrade...
