Autotrace Output

I have a large partitioned table and I did an autotrace on it and I am having a hard time figuring out a couple of things. Here it is:

SQL>set autotrace traceonly
SQL>select count(*) from abc.mytable where value_date >= '01mar03';

Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=3487 Card=1 Bytes=8)
1 0 SORT (AGGREGATE)
2 1 SORT* (AGGREGATE) :Q223400
0

3 2 PARTITION RANGE* (ITERATOR) :Q223400
0

4 3 TABLE ACCESS* (FULL) OF 'MYTABLE' (Cost=3487 C :Q223400
ard=45581 Bytes=364648) 0



2 PARALLEL_TO_SERIAL SELECT /*+ PIV_SSF */ SYS_OP_MSR(COUNT(*)) F
ROM (SELECT /*+ NO_EXPAND ROWID(A2)

3 PARALLEL_COMBINED_WITH_PARENT
4 PARALLEL_COMBINED_WITH_PARENT


What is the PARALLEL_COMBINED_WITH_PARENT and the (Cost=3487 Card=1 Bytes=8)?

I have a Performance and Tuning book but the example they give is not like this. Is there a website or book that would better explain these outputs?

How many CPUs and disk controllers on ur box?
PARALLEL_COMBINED_WITH_PARENT -- this is parallel read operatior from the table
and ur have "parent" and set of "childs" parallel read processes
(perhaps from different partitions)