A handheld PC, or H/PC for short, is a computer built around a form factor which is significantly smaller than any standard laptop computer. It is sometimes referred to as a palmtop computer. Most handheld PCs use an operating system specifically designed for mobile use such as Microsoft's Windows CE. Ultra-compact laptops capable of running common X86-compatible desktop operating systems are typically classified as subnotebooks. The first hand-held device compatible with desktop IBM personal computers of the time was the Atari Portfolio of 1989. Other early models were the Poqet PC of 1989 and the Hewlett Packard HP 95LX of 1991. Other DOS-compatible hand-held computers also existed.