Difference Between Processes and Threads

On UNIX
Oracle Database uses a process to implement each of such background tasks as database writer (DBW0), log writer (LGWR), shared server process dispatchers, and shared servers. Each dedicated connection made to the database causes another operating system process to be spawned on behalf of that session.

On Windows
Each background process is implemented as a thread inside a single, large process. For each Oracle Database instance or system identifier, there is one corresponding process for Oracle Database. For example, 100 Oracle Database processes for a database instance on UNIX are handled by 100 threads inside one process on Windows.
All Oracle Database background, dedicated server, and client processes are threads of the master Oracle Database Windows process, and all threads of the Oracle Database process share resources. This multithreaded architecture is highly efficient, allowing fast context switches with low overhead.

To view processes or end individual threads, use Oracle Administration Assistant for Windows. Choose Start > Programs > Oracle - HOME_NAME > Configuration and Migration Tools > Administration Assistant for Windows. Right-click on the SID and connect and then choose Process Information.