The original PC design was followed up in 1983 by the IBM PC XT, which was an incrementally improved design; it omitted support for the cassette, had more card slots, and was available with a 10MB hard drive. Although mandatory at first, the hard drive was later made an option and a two floppy disk XT was sold. While the architectural memory limit of 640K was the same, later versions were more readily expandable.
