Oracle Database Design - Oracle 10g Database Administration Concepts and Implementation Made Simple - page 150

Before even we start DBCA we have to set some of the OS
environment variables. Those variables are mentioned below
along with the brief description.
ORACLE_BASE describes the top most directory where Oracle
software will be installed. In Windows environment we can set it
using the SET command. Let's suppose the DOS prompt is C:\>.
C:\> SET ORACLE_BASE C:\Oracle
Whereas in Unix we write the command as shown below.
% setenv ORACLE_BASE /Oracle
ORACLE_HOME specifies the directory that lies beneath
ORACLE_BASE and its here where Oracle products reside.
According to OFA (Optimal Flexible Architecture), this
environment variable should to set to
ORACLE_BASE/product/release#. Lets suppose the DOS
prompt is C:\>.
C:\> SET ORACLE_HOME C:\Oracle\database\9_2
Whereas in Unix we write the command as shown below.
% setenv ORACLE_HOME /Oracle/product/9_2
ORACLE_SID is the instance name or rather default instance
name on the machine having Oracle installed. This should be the
unique identifier of the Oracle Instance on the machine. A single
machine can have more than one instance, so each should be
having separate SID. Lets suppose the DOS prompt is C:\>.
C:\> SET ORACLE_SID test
Whereas in Unix we write the command as shown below.
% setenv ORACLE_SID test