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 Sony TX66 and Sony A55 side-by-side from the front, back and top in their relative dimensions. Sony TX66 has external dimensions of 93 x 54 x 13 mm (3.66 x 2.13 x 0.51″) and weighs 109 g (0.24 lb / 3.84 oz) (including batteries). Sony A55 has external dimensions of 124 x 92 x 85 mm (4.88 x 3.62 x 3.35″) and weighs 500 g (1.10 lb / 17.64 oz) (including batteries).
Below you can see the front-view size comparison of the Sony TX66 and the Sony A55. Sony TX66 is clearly the smaller of the two cameras. Its body is 31mm narrower, 38mm shorter and 72mm thinner than Sony A55. As you can tell, actually this is not a fair size comparison since Sony TX66 has a built-in lens but Sony A55 doesn't. Once you put a lens on A55, its thickness will increase significantly.
Here is the back view size comparison of the Sony TX66 and Sony A55.
Now lets look at the top view comparison of Sony TX66 and Sony A55.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Sony TX66 is significantly lighter (391g ) than the Sony A55 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 A55, the total kit will weigh much higher.
Weather Sealing
Unfortunately neither the Sony Cyber-shot DSC-TX66 nor Sony SLT-A55 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 Compact Cameras with Weather Sealing Top DSLR Cameras with Weather Sealing
LCD Screen Size and Features
Sony TX66's 3.30" LCD screen is slightly larger than Sony A55's 3" screen.