The x4 is a brilliant machine which is ideal to midi with keyboard or guitar as accompaniment which sounds as if you are part of a band with its realistic sounds.
The x4 is fitted with hard drive and also I had an updated ram which I bought separate from ketron which lets you store more patterns.
For technical information please look on the ketron website.
Also on the x4 which is not on newer models is that there are 4 separate outputs along with the standard stereo outs. This enables you to assign certain things for eg; like snare drum, bass guitar on separate outs or instruments giving you more control over your desired sound.
The ketron is in excellent condition no scratches or anything like that, that's the way I look after my gear. Also there as been a screen saver on the screen from new that's how fussy I am.  Case also in great condition.
Comes complete with ketron manual and mains lead.
There are hundreds of styles and songs in the machine to suit all tastes of music.
I can guarantee if this is what you are looking for you won't find a better one than this in the condition.