Data_Type2.htm
Ref :  11g release 2 ,3 PL/SQL Data Types

http://docs.oracle.com/cd/E11882_01/appdev.112/e25519/datatypes.htm#LNPLS003
Objective: PL/SQL Over SQL (ANSI ??)
Numeric data type supported by Oracle and PostgreSQL
SQL variable:
DB_BLOCK_SIZE :
Set this parameter at the time of database creation. Do not alter it afterward. 

Data Type 	Maximum Size	Maximum Size 
		Pl/SQL		SQL

CHAR 		32,767 bytes	2,000 bytes

NCHARF 		32,767 bytes  	2,000 bytes

RAW		32,767 bytes	2,000 bytes

VARCHAR2 	32,767 bytes	4,000 bytes

NVARCHAR2	32,767 bytes	4,000 bytes

LONG		32,760 bytes	2 GB- 1

LONG RAW	32,760 bytes	2 GB

BLOB		128 TB	 	(4 GB - 1) * db_block_size

CLOB		128 TB		(4 GB - 1) * db_block_size

NCLOB 		128 TB		(4 GB - 1) * db_block_size
This is a very fascinating area of know-how, http://docs.oracle.com/cd/B19306_01/server.102/b14237/initparams041.htm

The default value is 8192, not modifiable
The DB_BLOCK_SIZE is used to specify the standard block size which is used for the system and temporary tablespaces. The DB_BLOCK_SIZE parameter in your initialization parameter file determines the size of your standard block size in the database and frequently is the only block size for the entire database.

Database buffer cache size = DB_BLOCK_SIZE x DB_BLOCK_BUFFERS

manas8x_init_ora.txt
This segment of the current document is out of context, but I preferred to mention along with LBO data types. The init.ora file, contains important information concerning the structure of an oracle database installed in a typical PC.