sid in oracle 9i

SID---is the name of the database.
TNSNAMES.ORA-----This files contains the information which is used by the system to connect to oracle database.
TNS means Transparent Network Substrate (TNS)
This file is usually located at the following path.

.....\oracle\product\10.2.0\db_1\NETWORK\ADMIN

or

D:\oracle\ora90\NETWORK\ADMIN\tnsnames.ora

It contains several informations like

PROTOCOL
HOST IP ADDRESS
PORTNO
SID
etc


A typical entry in this file looks like this.
Expand|Select|Wrap|Line Numbers
1. MES =
2. (DESCRIPTION =
3. (ADDRESS = (PROTOCOL = TCP)(HOST = 10.35.15.1)(PORT = 1521))
4. (CONNECT_DATA = (SID = MES))
5.
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SID is the name of the Database to which we are connecting to
The full form of SID is SystemIdentifier which should be unquie in the TNS.ora file
TNS file contains info , through which the System connects to Oracle Database.

TNS file contains

1)PROTOCOL ( Mostly TCP..TransmissionControlProtocol)
2)HOST IP ADDRESS (Where the Database is resided ..Generally we call it as Server.Even the DSCP number acts as substitute)
3)PORTNUMBER ( 1521..Widely used by oracle)
4)SID (the name we provide for DataBase)
5)SERVER (Dedicated/Shared Which is defined at DB CREATION LEVEL)
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