I think this answers your question(Oracle v816, Concepts guide, Oracle intstance->MemoryArchitecture->SystemGlobalArea(SGA)):

"it must copy the data block from a datafile
on disk into a buffer in the cache before accessing the data."


"The first time an Oracle user process requires a particular piece of data, it searches
for the data in the database buffer cache. If the process finds the data already in the
cache (a cache hit), it can read the data directly from memory. If the process cannot
find the data in the cache (a cache miss), it must copy the data block from a datafile
on disk into a buffer in the cache before accessing the data. "