Also, the majority of mice on UI workstations used optical, not mechanical tracking during that time. Some of the higher end PC mice used optical tracking with the special printed aluminum mouse pad, but the mice with the ball inside were cheaper for them to produce, so that’s why you’ll see them on Consumer level computers of the era. The most common mice with optical sensors and a printed aluminum mouse pad were seen on sun workstations I believe the next cube Silicon Graphics workstations some Hewlett Packard, workstations and micro VAXes, but it was pretty rapid most companies, including workstation companies, moving to mechanical tracking mice, using the ball to move rollers Because it was a lot cheaper for them to produce and also you didn’t have to worry about the printed surface of the mouse pad, getting damaged and causing your mouse pointer to jump or in some cases with some of the older ones, the whole mouse could essentially crash where it would stop tracking altogether. If the damage to the mouse pad was bad enough been there done that wish I gotten the T-shirt.