I know this may sound dumb, but I have this HARD drive that I can figure out what it is.
 Quantum FIREBALL plus LM 3.5 series. From that how do I tell what size it is before putting it in an old computer ? Any help would be great.

Thanks!Exactly what markings are on the hard drive?  Anything that might indicate a specific model?  And, SEE http://www.google.com/search?hl=en&q=Quantum+Fireball+plus+LM+3.5+series&btnG=Google+SearchThanks for the help with Google. I done that before posting here.

All I have is

Quantum
Fireball Plus LM
3.5 series
N143
A jumper config
Bar code GTLA Lm15014-01-a 15. OAT

Thanks for any help.Might be easier to APPROACH from the computer angle.  Exactly what make and model computer is that?  And, why not connect that hard drive to that computer as a slave drive?  If you can get your comp to recognize the HD that way, you should be able to determine what size it is.I like soybean's idea of slaving it.
Then you could run Everest Home (Free) Edition to see exactly what it is.
And... that way you could run a diagnostic on it before you get too involved with it.
LACKING that, I would bet on 30GB if it's an LM.
See here:
http://www.active-hardware.com/english/reviews/storage/quantum-lm30.htm