OQO is a U.S. computer harware company, the manufacturer of subnotebook, handheld computers named the OQO model 02 and OQO model e2. Its systems possess the functionality of a tablet PC in a form-factor slightly larger than a PDA. According to Guinness World Records, the "OQO" is the smallest full-powered, full-featured personal computer. The company's first version of subnotebook computer is the OQO model 01. Recently, it has been compared with the Ultra Mobile PC platform, although it was introduced before the UMPC took flight. Apple Inc.'s (at the time Apple Computer, Inc.) refusal to let them develop a Model 1-like mobile Macintosh prompted many of OQO's original staff (creators of the "TiBook" Powerbook G4) to leave Apple and found the company. The UPCs are capable of running slightly modified versions of Linux or other x86 based operating systems.