?Mainframes are dead, long live Mainframes!? Ted Lewis, CEO of Assessment Group (TAG) commented. Mainframes are large computer systems to which different subsystems, as disk arrays or tape libraries, can be connected. For a while mainframes seemed to be a thing of the past. After reconsideration the result was exactly the opposite: these powerful computers are key players in large enterprises, they are the embodiment of performance, availability and security. One of the most significant mainframe is the IBM S/390. It is not just a computer, the S/390 stands for a whole computer series. It is used where more than one application is launched or a large amount of data has to be computed, or for server consolidation. The architecture of the S/390 processor is built for high performance. Today the S/390 series is completed by the zSeries. The construction of such a machine is impressive.

The S/390 or zSeries offers various connection facilities; ESCON, FICON, OSA-Express are some of IBM's high performance connection protocols to subsystems.

Also the software made huge progress over the last 20 years. Open and non-proprietary applications and operating systems are in great demand. IBM started an attempt to open their powerful OS/390, now called z/OS, to other systems. The evolution of this operating system over more than 30 years is impressive. Improved algorithms and applications led to a great enhancement of performance. These systems are nowadays so much sophisticated that they can partly configure and manage themselves. The question now is the following: How long will it take till such systems are completely autonomous?

IBM eServer iSeries is a server platform for the professional use in business key areas such as E-Commerce, Supply Chain Management (SCM) or Customer Relationship Management (CRM). iSeries-Server persuade with their high availability, good scalability and their balanced performance and meet high customer satisfaction thanks to modern technology and architecture. They are based on powerful 64-Bit RISC-Microprocessor and able to be divided into partitions, whereby the resources such as disc, memory and processor can be allocated to the partitions allowing the isolation of workloads.

This work describes the basics of technology, operating systems and areas of application of iSeries. It's addressed to those responsible for IT who'd like to get an overview on these server platforms as well as to the management to evaluate a new server platform. In the first part the hardware-architecture and the operating systems supported by the iSeries are being described. The rather technical part of our work will be completed by the chapter application development. This will be followed by usage area, evaluation criteria - which consists among others of a study about Total Cost of Ownership - and an example of a midrange company using the Enterprise Resource Planning (ERP) solution on iSeries.

IBM has come away from their proprietary image with the new model of the iSeries. They now support several operating systems and external devices of foreign suppliers. This makes iSeries a solid server platform. We believe however that IBM can't rest on their technological lead and shouldn't neglect the contact to clients of many years. In other words: the best invention is of no use if not communicated as such.