Editing Energy management system (section)

==Operating systems==
Up to the early 1990s it was common to find EMS systems being delivered based on proprietary [[Computer hardware|hardware]] and [[operating system]]s. Back then EMS suppliers such as [[Harris Corporation|Harris Controls]] (now [[General Electric|GE]]), [[Hitachi]], [[Cebyc]], [[Control Data Corporation]], [[Siemens]] and [[Toshiba]] manufactured their own proprietary hardware. EMS suppliers that did not manufacture their own hardware often relied on products developed by [[Digital Equipment]], [[Gould Electronics]] and [[MODCOMP]]. The VAX 11/780 from Digital Equipment was a popular choice amongst some EMS suppliers. EMS systems now rely on a model based approach. Traditional planning models and EMS models were always independently maintained and seldom in synchronism with each other. Using EMS software allows planners and operators to share a common model reducing the mismatch between the two and cutting model maintenance by half. Having a common user interface also allows for easier transition of information from planning to operations.

As proprietary systems became uneconomical, EMS suppliers began to deliver solutions based on industry standard hardware platforms such as those from [[Digital Equipment]] (later [[Compaq]], then [[Compaq|HP]]), [[IBM]] and [[Sun Microsystems|Sun]]. The common operating system then was either DEC [[OpenVMS]] or [[Unix]]. By 2004, various EMS suppliers including [[Alstom]], [[ABB Asea Brown Boveri|ABB]] and [[Open Systems International|OSI]] had begun to offer Windows based solutions. By 2006 customers had a choice of [[UNIX]], [[Linux]] or [[Microsoft Windows|Windows]]-based systems. Some suppliers including ETAP, NARI, PSI-CNI and Siemens continue to offer UNIX-based solutions. It is now common for suppliers to integrate UNIX-based solutions on either the Sun [[Solaris (operating system)|Solaris]] or IBM platform. Newer EMS systems based on [[blade server]]s occupy a fraction of the space previously required. For instance, a blade rack of 20 servers occupy much the same space as that previously occupied by a single [[MicroVAX]] server.