Buffer Pool caching in Sql clarification

I might sound a little naive to ask this question but I couldn’t find out the answer anywhere. So my understanding is that the buffer in a sql db maintains disk pages in cache so that when a query comes in and if the page is available in the cahce the data can be served without going to the disk. Now my question is that does the pages in bufferpool maintains the actual data (complete rows) and directly serves the data or it keeps the offset of the disk and whenever needed directly fetches from the offset. My earlier understanding was the former but when i was reading more I learnt about index organised tables and heap organised tables which made me confused about how it actually does or it could be both.