OS 4.55

I'm buying a used MPC, my first, and appreciate all the cool info in these forums. First question (hopefully not too stupid, but I'm a complete newby): the seller says it has OS 4.55. Does anyone know what that it? Is it a JJ OS version? Can anyone point me to info about that system, or problems with it if any?
Thanks very much.

Go to the Akaipro site : http://www.akaipro.com/mpc1000

See what OS version is available...and do the math.

The latest one is OS v2.13...so you are running JJOS.

Now go to the JJOS site and have phun... : http://www7a.biglobe.ne.jp/~mpc1000/