Difference Between Global Database Name and SID

Hi,
What is the difference between global database name and SID.

When you put in a value for globla database name it automatically populates the SID when using database configuration assistant. why ?
Infact why does it ask me for a global database name while installing 8i. Shouldnt it ask it while creating the database.

Thanks
Anurag

SID is the system Identifier and Global Database is databasename.domin . Usually we create database name with same SID.

By default ORACLE 8i creates a small database at the time of installation. That is the reason it will ask global database name and also takes first part of global database name as SID.