I tried to find this on the Juki website but its obviously a previous model so not much info on there. But did find it listed elsewhere as a 3/4 thread overlocker.
So I'd guess at the following, it probably seams a four thread marrow (overlock seam) made with two needles and two loopers. And a three thread overlock seam where you use either the left or right needle, this would give you either a narrow or wider 3 thread seam. Image below of 3 and 4 thread overlock seams.
Lastly, I would suggest that the D denotes Differential feed, this is a feature that controls the two feed dogs in the machine and gives you the ability to set them to move at different speeds - very handy to control the fabric feeding but also used decoratively for lettuce edging.
Rolled hem - most overlockers of 3/4 variety will also do a rolled hem; however, I can't actually confirm if this model does or not. But look around for a retractable stitch ****** in the foot or needle plate or a second needle plate in the accessory case. Rolled hemming is also very useful and most models will do it now; just variation in how you actually set it up to do so. Bernettes you flick a lever in front of the needle/foot area, earlier Elnas like the L3 and L4 you needed to change the needle plate and a little ****** in the presser foot.
Of course, you could email the local distributor for Juki in your country and ask them and this may be the best way to check. Just copy this into your browserhttp://www.juki.co.jp/juki_form/home_e/toiawase_form.html
to go to their contact us page.