Internal Operations on LIMIT & OFFSET clause

Hi Friends,

        I have one doubt in LIMIT & OFFSET clause operation.
I have a table "test_limit",  and it contain,

SELECT * from test_limit;
 s_no |    name
------+-------------
    1 | anbarasu
    8 | egambaram
   12 | jyothi
    6 | mahalakshmi
    4 | maheswari
    2 | manju
    5 | ramkumar
    7 | sangeetha
   11 | sasikala
   10 | thekkamalai
    9 | vivek
   13 | ganeshwari
    3 | anandhi
(13 rows)

Here, I applied LIMIT clause as bellow.
SELECT * from test_limit LIMIT 5;
 s_no |    name
------+-------------
    1 | anbarasu
    8 | egambaram
   12 | jyothi
    6 | mahalakshmi
    4 | maheswari
(5 rows)

In this above query was processed only five records  OR all the 13 record was got and then only 5 record printed.
this is what my doubt.

I tried where clause in above query as bellow.
SELECT * from test_limit where s_no IN (1,2,3,4,5,6,7,8,9) LIMIT 5;
 s_no |    name
------+-------------
    1 | anbarasu
    8 | egambaram
    6 | mahalakshmi
    4 | maheswari
    2 | manju
(5 rows)

In this case It should process up to  records fulfill the requirement.
i.e  atleast it should process 6 records.
My question is it is processed only 6 records (fulfill the requirement) or all (13) the records.

I also tried ORDER BY clause as bellow.
SELECT * from test_limit ORDER BY s_no LIMIT 5;
 s_no |   name
------+-----------
    1 | anbarasu
    2 | manju
    3 | anandhi
    4 | maheswari
    5 | ramkumar
(5 rows)

From this output, I know it is processed all(13) the records and the printed only 5 records.
But, without ORDER BY clause I don't know how many record processing when applying LIMIT clause.

---
Vanitha Jaya