do you have to buy the screen by part number or can you buy it by size?
Part number. There are too many variables to just grab on on size:
* Backlight type (CCFL (one (most common) or two bulb) or LED)
* Resolution of screen (1366x768, 1600x900, etc)
* Aspect ratio (16:9 16:10, not too much of an issue since they are making them different sizes: 15.6 vs 15.4)
* Type of connector (different number of pins, different sizes)
* Position of connector (left, right, top, bottom (had a 14" screen laying around I wanted to put in a dell, it barely works only because of the video cable being a SOLID board! shaped to go exactly where they want it)
* Built in mounting, or inverter bracket
* Glossy or Matte?
I think those are all the highlights