The Nikon D70 and Nikon D70s are two different kinds of camera with several similar features; just the latter has some added or improved features. Foremost, the D70s possesses a LCD Display of 2.0 inch at the rear which provides a display that is slightly bigger than the other one so as to view images better.
On the other hand, the Nikon D70 is of 1.8 inch LCD Display. Though there is only a slight difference of 0.2 inch, but it is noticeable in the output of the two devices. Another difference to mention between the two cameras is the battery present in them.
The Nikon D70 has the EN-EL3 battery in them, while the Nikon D70s uses the EN-EL3a battery. This simply means the D70s has a stronger battery that lasts longer, which makes it to take more shot that its counterpart. The images that are taken with the D70s are also seen to be sharper than the ones of d70.