database size

Hi,

I created a table with two columns of type int, and loaded about 300 K records
in it. So, the total size of the table is approx. that of 600 K integers,
roughly 2.4 MB.
But, the file corresponding to the table in pgsql/data/base directory
has a size of 19 MB. I was wondering if I have done something wrong in
the installation or usage, or is it the normal behavior ?

Also, I was trying to execute the query:
select item as item, count(*) as cnt into table C_temp
from temp group by item;

Here, temp is the name of the table which contains the data and item is an
integer attribute. While doing the sort for the group by, the size of one of
the temporary pg_psort relation grows to about 314 MB. The size of the temp
table is as mentioned above. If someone tried similar queries, could you
please tell me if this is normal.
The above query did not finish even after 2 hours. I am executing it on a
Sun Sparc 5 running Sun OS 5.5.

Thanks
--shiby