oracle adapter settings

Hi,
when I was reading docs about rails + oracle I met 2 different ways to
setup using oracle db in the database.yml file:
for example,

development:
adapter: oracle
database: 192.168.0.100/orasid
username: test
password: test

and

development:
adapter: oci
host: 192.168.0.100/orasid
username: test
password: test

please, explain me what is the difference in ?
Thanks.