PC-based IBM mainframe-compatible systems

The S/390 Integrated Server (short for System/390 Integrated Server) was a low-end IBM mainframe offering in the mid-1990s. Unlike other ESA/390 mainframes, the S/390 Integrated Server was actually an S/390 processor card installed in an IBM PC Server or RS/6000. Another unusual feautre in the mainframe world was its use of internal DASD, although external storage was also available.. It came in two varieties, the POWER-based R/390 and the Pentium-based P/390.

S/390 Processor Card

An important goal in the design of the S/390 Processor Card was complete compatibility with existing mainframe operating systems and software. The processor implements all of the ESA/390 and XA instructions which prevents the need for instruction translation. The S/390 Processor Card also incorporated 32MB of dedicated memory with an optional 96MB daughter card for a combined total of 128MB of RAM. The processor was officially rated at 4.5 MIPS.

R/390

R/390 was the designation used for the expansion card used in an IBM RS/6000 server. The R/390 featured a 67 MHz or 77 MHz POWER 2 processor and 32MB to 512MB of RAM, depending on the configuration. R/390 servers required AIX to be run as the host operating system.

P/390

P/390 was the designation used for the expansion card used in an IBM PC Server and was less expensive than the R/390. The original P/390 server was housed in an IBM PC Server 500 and featured a 90 MHz Intel Pentium processor for running OS/2. The model was revised in mid-1996 and rebranded as the PC Server 520, which featured a 133 MHz Intel Pentium processor. Both models came standard with 32MB of RAM and were expandable to 256MB. The PC Server 500 featured eight Micro Channel expansion slots while the PC Server 520 added two PCI expansion slots and removed two Micro Channel slots.

Uses

The S/390 Integrated Server was not a particularly powerful mainframe, even when it was released. It was commonly used for development and as a cheaper replacement of older mainframes. It was capable of running OS/390 as well as older 24-bit operating systems, but due to its inherent 31-bit design, can not run current versions of z/OS.