What's instance, ROWID and why we use cursor?

Dear memebers,
yesterday i have an interview there i faced the following questions.
1. what is instance?
2. what is ROWID?
3. why we use cursor?
i can give only the last one.
i am waiting for your answer.
thanks
Regards:
Muhammad Nadeem
[email protected]

HY
Row Identifiers
Each row in an Oracle database has a unique row identifier, or rowid, which is used internally by the Oracle database to access the row. A rowid is an 18-digit number that is represented as a base-64 number, and it contains the physical address of a row in an Oracle database. You can view the rowid value for rows in a table by specifying the ROWID column in the select list of a query. The query in the following example retrieves the ROWID and customer_id columns from the customers table:
SELECT ROWID, customer_id
FROM customers;
Oracle instance:
An Oracle instance is the combination of the background processes and
memory structures. The instance must be started to access the data in the database. Every
time an instance is started, a System Global Area (SGA) is allocated and Oracle
background processes are started. Background processes perform functions on behalf of
the invoking process. They consolidate functions that would otherwise be handled by
multiple Oracle programs running for each user. The background processes perform
input/output (I/O) and monitor other Oracle processes to provide increased parallelism
for better performance and reliability.
REGARDS

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Message was edited by: Trent Mckenica
Message was edited by: Trent Mckenica

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