The PowerBook 500 series laptops introduced the “trackpad” to the Macintosh: the cursor followed the movement of your finger on a pad rather than spinning a plastic trackball with your finger. The trackpad has proven to be a revolutionary input device and has been used since in most notebooks. The PowerBook 500 series also introduced the idea of dual-swappable bays that could be used to hold either one battery and a PCMCIA adapter or two batteries.
The Macintosh PowerBook 540 featured a 33 MHz 68LC040 processor, 8 MB or 12 MB of RAM, and a 240 MB hard drive. The screen was a 9.5-inch grayscale active-matrix display.
The PowerBook 540 was similar to the PowerBook 520 that was being offered at the same time, but the PowerBook 540 had a faster processor and a higher quality active-matrix display.