The PowerBook 165C's modem slot doubles as a PCMCIA gateway

Vintage Macs had a different idea of “upgradeable.” The PowerBook 165C’s internal modem (if equipped) can be pulled out and replaced with a compatible PCMCIA or ExpressCard adapter via the single Type II PC Card slot. That slot was ahead of its time — it gave a 33 MHz 68030 laptop a pathway to peripherals that outlived the machine itself.

Also worth noting: the trackball is user-serviceable. You can clean it or replace it, which was handy back when trackballs collected desk grit like a magnet. It’s a small thing, but it means this 1993 laptop still has some life left in its input system if you’re willing to get your hands dirty.