Oracle Tips  by Burleson Consulting

The Data Warehouse Development Life Cycle

Parallelism And Oracle Data Warehousing
Oracle Parallel Database And Server
In general, a parallel database is defined as a database that has several memory regions that share a common disk drive. Within Oracle, several Oracle instances run within RAM memory, and each independent instance shares access to the same Oracle tables. Within the Oracle parallel server, this is called the shared-nothing parallel server configuration. Figure 7.6 shows a shared-nothing parallel server configuration.

Figure 7.6 A shared-nothing parallel server configuration.

Oracle also supports symmetric multiprocessing (SMP) configurations where a single host contains multiple processors (see Figure 7.7). In SMP configurations, we see that the multiple processors will provide concurrent processing, but that all of the processors must share a common buffer pool. In short, a symmetric multiprocessor configuration is one where a number of processors share common memory and disk resources.

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This is an excerpt from "High Performance Data Warehousing". To learn more about Oracle, try "Oracle Tuning: The Definitive Reference", by Donald K. Burleson.  You can buy it direct from the publisher at 30% off here:
http://www.rampant-books.com/book_1002_oracle_tuning_definitive_reference_2nd_ed.htm