* PGA memory allocation depends on whether the database uses dedicated or shared server connections.

Note:
*System global area (SGA) The SGA is a group of shared memory structures, known as SGA components, that contain data and control information for one Oracle Database instance. The SGA is shared by all server and background processes. Examples of data stored in the SGA include cached data blocks and shared SQL areas.
*Program global area (PGA)
A PGA is a memory region that contains data and control information for a server process. It is nonshared memory created by Oracle Database when a server process is started. Access to the PGA is exclusive to the server process. There is one PGA for each server process. Background processes also allocate their own PGAs. The total memory used by all individual PGAs is known as the total instance PGA memory, and the collection of individual PGAs is referred to as the total instance PGA, or just instance PGA. You use database initialization parameters to set the size of the instance PGA, not individual PGAs.
Reference: Oracle Database Concepts 12c

Explanation/Reference:
Explanation:
"Oracle Grid Infrastructure for a standalone server includes Oracle Restart and Oracle Automatic Storage Management. Oracle combined the two infrastructure products into a single set of binaries that is installed into an Oracle Restart home."
References: http://docs.oracle.com/cd/E16655_01/install.121/e17735/oraclerestart.htm#NTDBI999

A:Variable size extents enable support for larger ASM datafiles, reduce SGA memory requirements for very large databases(A), and improve performance for file create and open operations.
C:You don't have to worry about the sizes; the ASM instance automatically allocates the appropriate extent size.
Note:
*The contents of ASM files are stored in a disk group as a set, or collection, of data extents that are stored on individual disks within disk groups. Each extent resides on an individual disk.
Extents consist of one or more allocation units (AU).
To accommodate increasingly larger files, ASM uses variable size extents.
*The size of the extent map that defines a file can be smaller by a factor of 8 and 64 depending on the file size. The initial extent size is equal to the allocation unit size and it increases by a factor of 8 and 64 at predefined thresholds. This feature is automatic for newly created and resized datafiles when the disk group compatibility attributes are set to Oracle Release 11 or higher.

RMAN> ALTER TABLESPACE sysaux OFFLINE IMMEDIATE;
RMAN> RESTORE TABLESPACE sysaux;
RMAN> RECOVER TABLESPACE sysaux;
RMAN> ALTER TABLESPACE sysaux ONLINE;
* Example:
While evaluating the 12c beta3 I was not able to do the recover while testing "all pdb files lost".
Cannot close the pdb as the system datafile was missing...
So only option to recover was:
Shutdown cdb (10)
startup mount; (1)
restore pluggable database
recover pluggable database
alter database open;
alter pluggable database name open;
Oracle support says: You should be able to close the pdb and restore/recover the system tablespace of PDB.
* Inconsistent backups are usually created by taking online database backups. You can also make an inconsistent backup by backing up data files while a database is closed, either:
/ Immediately after the crash of an Oracle instance (or, in an Oracle RAC configuration, all instances)
/ After shutting down the database using SHUTDOWN ABORT
Inconsistent backups are only useful if the database is in ARCHIVELOG mode and all archived redo logs created since the backup are available.
*Open the database with theRESETLOGSoption after finishing recovery:
SQL> ALTER DATABASE OPEN RESETLOGS;

Example (see step23):
Step 1:
Run the RMAN FLASHBACK DATABASE command.
You can specify the target time by using a form of the command shown in the following
examples:
FLASHBACK DATABASE TO SCN 46963;
FLASHBACK DATABASE
TO RESTORE POINT BEFORE_CHANGES;
FLASHBACK DATABASE TO TIME
"TO_DATE('09/20/05','MM/DD/YY')";
When the FLASHBACK DATABASE command completes, the database is left mounted
and recovered to the specified target time.
Step 2:
Make the database available for updates by opening the database with the RESETLOGS
option. If the database is currently open read-only, then execute the following commands in
SQL*Plus:
SHUTDOWN IMMEDIATE
STARTUP MOUNT
ALTER DATABASE OPEN RESETLOGS;