The personal computer (PC) defines a computer designed for general use by a single person. While an iMac is definitely a PC, most people relate the acronym to computers that run on the Windows operating system instead. PCs were first known as microcomputers because they were complete computers but built on a smaller scale than the huge systems in use by most businesses.
In 1981, iconic tech maker IBM unveiled its first PC, which relied on Microsoft's now-legendary operating system — MS-DOS (Microsoft Disk Operating System). Apple followed up in 1983 by creating the Lisa, one of the first PCs with a GUI (graphical user interface) [sources: Alfred, Cabell]. That's a fancy way of saying "icons" were visible on the screen. Before that, computer screens were pretty plain.
Along the way, critical components such as CPUs (central processing units) and RAM (random access memory) evolved at a breakneck pace, making computers faster and more efficient. In 1986, Compaq unleashed a 32-bit CPU on its 386 machines. And of course, Intel grabbed a place in computer history in 1993 with its first Pentium processor [sources: PCWorld, Tom's Hardware].
Now, personal computers have touchscreens, all sorts of built-in connectivity (like Bluetooth and WiFi), and operating systems that morph by the day. So do the sizes and shapes of the machines themselves.