These databases are operated by a set of computers and servers, and come in handy during medical alerts and emergencies. The concept of EHR is a bit broader than the EMR, as the database is accessible from different clinics and hospitals. Thus, a patient's medical history can be retrieved from any hospital by an authorized medical practitioner.
Read more at Buzzle: http://www.buzzle.com/articles/uses-of-computers-in-hospitals.html