Size and weight are big decision factors when you are trying to find the ideal camera for your needs.
In this section, we are going to illustrate the Nikon D80 and Pentax X90 side-by-side from the front, back and top in their relative dimensions. Nikon D80 has external dimensions of 132 x 103 x 77 mm (5.2 x 4.06 x 3.03″) and weighs 668 g (1.47 lb / 23.56 oz) (including batteries). Pentax X90 has external dimensions of 111 x 85 x 110 mm (4.37 x 3.35 x 4.33″) and weighs 428 g (0.94 lb / 15.10 oz) (including batteries).
Below you can see the front-view size comparison of the Nikon D80 and the Pentax X90. Pentax X90 is 21mm narrower and 18mm shorter than Nikon D80 but it is also 33mm thicker. As you can tell, actually this is not a fair size comparison since Pentax X90 has a built-in lens but Nikon D80 doesn't. Once you put a lens on D80, its thickness will increase significantly.
Now lets look at the top view comparison of Nikon D80 and Pentax X90.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Pentax X90 is significantly lighter (240g ) than the Nikon D80 which may become a big advantage especially on long walking trips.
Again, this comparison may not be very useful in real life as we are comparing the weight of a camera with a built-in lens to the body-only weight of an interchangeable lens camera. Once you put a lens on D80, the total kit will weigh much higher.
Weather Sealing
Unfortunately neither the Nikon D80 nor Pentax X90 provides any type of weather sealing in their bodies, so you have to give extra care especially when you are shooting outdoors. If weather sealing is a must-have feature for you, check these sections: Top DSLR Cameras with Weather Sealing Top Bridge Cameras with Weather Sealing
LCD Screen Size and Features
Pentax X90's 2.70" LCD screen is slightly larger than Nikon D80's 2.5" screen.
Unfortunately, both cameras has fixed screens so they don't tilt or flip in directions.