Mac OS 7.5.2, also known as System 7.5.2, accompanied the first four PCI-based Power Macs and the PowerBook 5300 line in the summer of 1995. (PowerBook 500 series portables with a PowerPC upgrade could also run this version of the Mac OS.) It could not be used on any other Mac. This version was released to address the new hardware features on these new Macintosh models. The update was released just five short months after the introduction of Mac OS 7.5.1.