a p28 ecu is a ecu off of a 94-95(not sure wat years) civic ex.. its a sohc vtec computer.. people like to run a p28 because its easy to chip and tune.. obd2 computers cant.. also it looks for less sensors.. like the second o2 sensor and the knock sensor.. if u plan on gettin a p28 u will need a obd2b to obd1 jumper harness which ebay sells for cheap.. well thats all i can think of on the top of my head..