Difference between Oracle Single instance and Oracle RAC

Single  Instance	Oracle RAC
Single instance accessing database	Multiple instances accessing same database
Database can be local or shared	Database must be on shared.
Minimum one node is Required	Minimum two node required
Clusterware software is not required	Clusterware Software is required.
Consists of one SGA and one set of background  processes	Each instance having own  one SGA and one set of background  processes
One set of redo logs	Multiple set redo logs depending on number of instances
No Cache fusion used un Single instance	Cache fusion is used to transfer or access block from remote instance
V$ views to monitor and manage instance	For monitoring at the cluster level Oracle provides GV$ views.
Meeting some of the business requirements (availability, scalability) is limited to a single instance configuration.	Modern business requirements of high availability and linear scalability are provided by multiple instances sharing a common physical database