A personal computer (PC) is any computer whose original sales price, size, and capabilities make it useful for individuals, and which is intended to be operated directly by an end user, with no intervening computer operator.
Today a PC may be a desktop computer, a laptop computer or a tablet computer. The most common operating systems are Microsoft Windows, Mac OS and Linux, while the most common microprocessors are x86-compatible CPUs.
Microsoft's advertising campaign is a fail... They could be advertising either Mac OS, Microsoft Windows, or Linux...