Content by William R. Walsh, original here.
The IBM PS/2 Model 25 personal computer is an all-in-one unit. The monitor and computer are in one case. In order to get a feel for what your particular system is capable of, you need to find out what is inside. In a perfect world, all the model numbers would be unique and well documented. This being IBM, however, that isn't the case. For the best possible assessment of what you have (or don't have), the best thing you can do is open your system unit (see the instructions here) and take a look at it. This will answer your questions and builds your character (maybe).
Three specific systems and one upgrade model number exist as provided by IBM. All four systems differ greatly in planar (mainboard) design, processing speed, display, storage capability, and upgrade parts that can be used. I've seen conflicting labeling on systems and sometimes people do strange things, such as swapping monitor assemblies with a lower end system.
Should you desire to see your system's type-model and serial number, you will find them on a label underneath the lower left hand corner of the monitor bezel. The system should be facing you, as in the picture below.