Partitions and work_mem?

I'm running Postgres 8.4 on RHEL 6 64-bit and I had a question about how
work_mem and partitions interact.

https://wiki.postgresql.org/wiki/Tuning_Your_PostgreSQL_Server#work_mem
The above wiki states that "if a query involves doing merge sorts of 8
tables, that requires 8 times work_mem." If I have a table that is
partitioned does each partition count as a "table" and get its on work_mem?

For example, say I have the following table partitioned by the time column:
CREATE TABLE values (time TIMESTAMP, value INTEGER);
If I do the following query will it require 1 work_mem or N work_mem's
(where N is the number of partitions)?
SELECT * FROM values ORDER BY time;

Thanks,
Dave