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 Canon SD990 IS and Pentax K20D side-by-side from the front, back and top in their relative dimensions. Canon SD990 IS has external dimensions of 98 x 62 x 28 mm (3.86 x 2.44 x 1.1″) and weighs 205 g (0.45 lb / 7.23 oz) (including batteries). Pentax K20D has external dimensions of 142 x 101 x 70 mm (5.59 x 3.98 x 2.76″) and weighs 800 g (1.76 lb / 28.22 oz) (including batteries).
Below you can see the front-view size comparison of the Canon SD990 IS and the Pentax K20D. Canon SD990 IS is clearly the smaller of the two cameras. Its body is 44mm narrower, 39mm shorter and 42mm thinner than Pentax K20D. As you can tell, actually this is not a fair size comparison since Canon SD990 IS has a built-in lens but Pentax K20D doesn't. Once you put a lens on K20D, its thickness will increase significantly.
Here is the back view size comparison of the Canon SD990 IS and Pentax K20D.
Now lets look at the top view comparison of Canon SD990 IS and Pentax K20D.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Canon SD990 IS is significantly lighter (595g ) than the Pentax K20D 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 K20D, the total kit will weigh much higher.
Weather Sealing
Thanks to the weather-sealed body of the K20D, you can use this camera with more confidence under conditions where there is risk of exposure to water and dust compared to the SD990 IS.
LCD Screen Size and Features
Pentax K20D's 2.70" LCD screen is slightly larger than Canon SD990 IS's 2.5" screen.
Unfortunately, both cameras has fixed screens so they don't tilt or flip in directions.