Micro IBM mainframes

I have a couple of IBM’s microcomputer-based implementations of their mainframe architecture, plus an IBM XT/370 card set that does not work (it has a bad M-Card).


One of my two working “mainframes” is an IBM PC XT/370. The XT/370 is a PC XT (or, equivalently, a PC with the 256KB mother board and a hard drive), with the PC XT/370 card set and, somewhat optionally, an IBM 3277 emulation adapter.

The PC XT/370 card set comprises two cards: the processor, or P-Card and memory card, or M-Card.

My PC XT/370 did not start out life as an XT/370. Instead it was “cobbled together” (before I acquired it), using an IBM PC/XT with the requisite 256KB of memory on the mother board and the X/370 card set which I acquired separately in 2013. It also has a 3rd-party 20MB Seagate hard disk with its own adapter, and a 3.5″ floppy diskette.

It supports special IBM software, VM/PC that has a somewhat cut-down version of the IBM VM Control Program (CP) and Conversational Monitor System (CMS).

IBM P/390E Card

My other “mainframe” is a PC with an IBM P/390E card. This PCI card is capable of acting as an IBM 370 mainframe or as a S/390 mainframe. It is fully capable – it will run the “stock” IBM operating systems.

Ordinarily this card would be installed in an IBM PC Server 330. Not having one of those handy, I originally used a similar era Pentium II based computer – the same one that I use for capturing floppy disks – but running under OS/2 in this case.

In 2021, I replaced the hard drives on my Pentium II with SSD’s. Running OS/2 on an SSD is reminiscent of the old cartoon that showed MVS as a turtle, with a snail labeled IMS on its back (“Wheeeeeeeee”). You can read about this adventure here. This first set of photos shows the card, and my original Pentium II setup.

Having accomplished that, I then moved the P/390E card to a PC running on a 1.33 GHz AMD Athlon II, which supports a full 240GB SSD, and upgraded from OS/2 Warp 3 to Warp 4.52, shown in the photos below: