Oracle database architecture tutorial

Oracle Instance

An oracle instance is a set of different memory structures and the processes which manages all database activities, such as transaction processing, database recovery, form generation, and so on. There is different type of memory block which are accessed by different type of background processes

SGA :

It is also commonly known as  System Global area. It solve many purpose like storing parsed SQL qyeries/ Parsed Pl-sqL code and redo buffer cache.

It has below memory pools

• shared pool : 
• Data Dictionary Cache:
• Buffer Cache:
• Redo Log Buffer:
• Large Pool:
• Java Pool :

PGA :

Although the result of SQL statement parsing is stored in library cache, but the value of binding variable will be stored in PGA. Why? Because it must be private or not be shared among users. The PGA is also used for sort area.

Oracle Background Process:

There some back ground process which keep on running to fulfill DB requests.

• DBWR
• LGWR
• CKPT
• SMON
• PMON
• ARCH
• DISPATCHER PROCESSES
• RECO
• SNPn
• LCKn
• Pnnn

Thanks for reading article !! I found a full explanation of these component here