What do those codes actually mean? Is the first number and letter like a version number and the second number like the type?

Sorry to get back into this one again but how do i know what type of chip to use? The main reason im using a PIC16F84A is because ive used it in the past and its always worked fine. I dont like thinking that way. Im all for changing to make things better but here i dont know what to change to. You have given me a few examples but how did you know which ones do the same thing? I know the datasheets tell you but i dont believe that you sit there reading every possible datasheet to find the chip you want

I think ill stick with 3 pin ones then. I dont want any extra components taking up room/money.