The P/390 is basically an IBM mainframe system adapted to run on a personal computer. A P/390 comes on a single card that contains a System/390 instruction set, allowing operating systems such as OS/390, MVS, VM, and VSE, to be installed. The P/390 makes it possible to develop, test, and run application programs written for the mainframe on a smaller, more economical machine. After testing, programs that require mainframe capability can be moved to the mainframe. A common use of the P/390 today is for 2000 analysis and testing. The P/390 is sold as part of a PC workstation that also comes with an OS/2 operating system. The entire product is called the IBM PC Server System/390. The MVS and OS/390 operating systems require 128 megabyes of RAM. VM and VSE will install with 32 megabytes.
An R/390 is the P/390-PCI card installed on IBM's RS/6000 server. Both products are sold both as development environments and as economical approaches for companies with older mainframe systems to move their legacy applications to a new production environment.