ThinkPad 500 series
The 500 series was developed as a compact subnotebook machine line. This was to fill in the gap of a very portable, but still reasonably powerful laptop.
As the models were made as thin and light as it could be, it had to naturally exclude the floppy drive and the optical drive from its design. That shortfall was easily fixed however, as the late introduction of a docking port gave it the ability to use optical drives or floppy drives. Although, it came with the disadvantage of being thicker and heavier.
Following the discontinuation of every numerical series ThinkPads, the 500 series was replaced with the X series as its successor.