i see the phyical size of CCD sensors listed as 1/2.5", what does that mean?
It means the manufacturer is obfuscating and does not really want you to know precisely what the real dimensions in inches or centimeters are. Fortunately some do put the actual size in millimeters somewhere in an obscure part of their documentation, or some enterprising technical reviewer actually measures the sensor's size if it is at all accessible.
A sensor of the type 1/2.5" has an aspect ratio (width/height) of 4:3, a width of 5.760mm, a height of 4.290mm and a diagonal of 7.182mm. Although this information is not at every photographer's immediate disposal, it is relatively easy to find on the web. One good source is: