What was the difference between Thomas Newcomen's and James Watt's steam engine?.

The steam engine of Thomas Newcomen and James Watt used the same principle of creating a vacuum and using steam to drive the device. The difference is that in James Watt's version, he uses a separate condenser to allow for a much greater efficiency in terms of power. The main difference with a separate condenser is that with a separate condenser, the main device can remain hot at all times, thus increasing efficiency.