Firstly, although IBM no longer provides support for upgrading AS/400s and iSeries servers, there are companies who can help. The lowest cost option is to extend the capabilities of an existing server with refurbished expansion units. These can be bought with installation and support contracts, and may extend the useful life of existing infrastructure. An iSeries IBM 9406, #5095 Storage/PCI Expansion Tower contains seven PCI-X IOP/IOA slots and supports up to 12 disk units. If your business's needs can be accommodated by the simple addition of an expansion unit, you may well get a few more years out of your old AS/400 system.
The second option is to upgrade to a newer model in the iSeries generation. Again, IBM no longer offers these servers but they can be bought refurbished at a reasonable price, and a late model iSeries system offers a significant boost in performance when compared to AS/400s from the early 1990s. A refurbished iSeries Model 810 will easily outstrip an earlier model AS/400, and they are eligible for IBM maintenance contracts.
The third option is to replace aging servers with a modern model from the Power Systems range. Technology has advanced considerably in the last decade and Power Systems, especially those with Power 9 chips, bring with them a host of revolutionary improvements in server technology. A POWER8 or 9 System can bring you much more substantial computing power/CPW for a fraction of the maintanence costs.
Whichever upgrade option a business chooses, Midland Information Systems can help with advice, support, and hardware. We have extensive experience in IBM systems from older AS/400s to the cutting-edge Power systems.