qiskit/releasenotes/notes/1.0/psutil-dependancy-removed-b...

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---
upgrade:
- |
The dependency on `psutil <https://pypi.org/project/psutil/>`__ has been removed. The
psutil library was previously only used for detecting the number of physical CPUs and
total system memory, however this information provided does not add sufficient value
to justify the additional dependencies and overhead so it has been removed. This does
mean that the default number of processes used by :func:`.parallel_map` and functions that
internally can use :func:`.parallel_map` such as :func:`.transpile` and :meth:`.PassManager.run`
may use more or less parallel processes than in previous releases. If you'd like to adjust the
number of processes used you can use the new ``num_processes`` argument to those functions, or
the ``QISKIT_NUM_PROCS`` environment variable or ``num_processes`` field in a user configuration
file (see the `local configuration guide
<https://docs.quantum.ibm.com/guides/configure-qiskit-local>`__
for more details) if you need to adjust the number of processes that Qiskit potentially uses.