question about performance of libpq

hi,all. A strange question is as follows:

I have two PCs:
machine A: FreeBSD 5.4 with PostgreSQL 8.1.2
machine B: Windows XP with PostgreSQL 8.1.2

A and B are with same hardware configuration and in a 100Mbit LAN.

a large table "lineitem" about 600572 rows exists in both A and B.

On machine B, i run psql and issue a sql "select * from lineitem" to A: 
the execution time is about 10s.
On machine A, i run psql and issue