IBM Trackball Keyboards
From Deskthority wiki
|Product family||IBM Model M|
|Keyswitches||Buckling spring over membrane|
|Interface||PS/2 × 2|
The Model M5-1 placed the trackball and four buttons between the cursor keys and the upper navigation block.
The Model M5-2 placed the trackball and eight buttons (four top, four rear) at the top-right of the keyboard, behind the LED panel.