04/P means that microchip recommends that this specific part should be used with a crystal having a maximum frequency of 4MHz and the package of the part is Plastic DIP
04/SP means the same as far as the frequency is concerned but SP tells you that the package is a skinny plastic DIP.
in I/SP the I means that the part is an industrial grade part and i have already told you about the SP
The package information for each of Microhip's device families can usually be found in the data sheets. Visit their website https://www.microchip.com/ and take a look at the product pages. There will be links specifc to each device family e.g.: **broken link removed** A very user friendly website IMHO