Which type of computer is specifically designed to sit compactly on a desk?

The correct choice, Desktop Computer, is specifically designed to be compact and suitable for sitting on a desk. Desktop computers typically consist of separate components, including a monitor, a system unit, and peripherals like a keyboard and mouse, all of which can be arranged neatly on a desk. The design of desktop computers allows for easy access to these components while providing the power and functionality necessary for typical computing tasks.

In contrast, personal computers encompass a broader category that includes desktops, laptops, and other forms. Notebook computers, while portable and compact, are designed for mobility and can be easily transported rather than specifically designed to occupy desk space. Tablet PCs prioritize touch interface and mobility, making them less suited as stationary desk units. Therefore, Desktop Computers are the most appropriate choice for the requirement of being designed to sit compactly on a desk.