FLEX-ES
FLEX-ES is software from Fundamental Software, Inc. that enables S / 390 operating systems to be operated on PC servers. With the help of this emulator , the IBM operating systems z / OS , z / VM and VSE / ESA can be operated unmodified on a PC server.
A license must be purchased to use FLEX-ES. With the purchase of the license, the user receives a dongle , which must be installed during operation.
The system components belonging to the above-mentioned operating systems can also be operated unmodified. Ultimately, this means that any application programs written for the S / 390 architecture can also be executed on an Intel computer without modification.
IBM permits the use of the named operating systems with FLEX-ES on Intel computers under license law. However, a license release is linked to the use of certain Intel processors. The use of FLEX-ES is approved for the range of applications from around 16 to 100 MIPS (million instructions per second).
Since IBM below about 26 MIPS no processors of such system architecture offers (more), especially those companies use this possibility, for historical reasons, extensive and complex own applications in S 390 / have developed and for a change to a different operating system architecture very extensive costs for new developments would be associated.