Can I install Oracle server and client on the same machine?

Can I have multiple Oracle clients on same machine?

The Oracle Universal Installer supports the installation of several active Oracle homes on the same machine as long as the products support this at runtime. You can have multiple versions of the same product or different products running from different Oracle homes concurrently.

Can Oracle 11G and 12c clients coexist?

That 11g and 12c are not compatible.

Can I install two versions of Oracle Database?

Yes, it is possible. Oracle Database supports multiple Oracle homes. You can install this release or previous releases of the software more than once on the same system, in different Oracle home directories. This allows flexibility in deployment and maintenance of the database software.

Is Oracle client a server?

The Oracle Client/Server Architecture The client executes the database application that accesses database information and interacts with a user through the keyboard, screen, and pointing device such as a mouse.