By Jakob Nielsen: sidebar to column on Mobile Site vs. Full Site.
Desktop computers (and laptops) mainly use a mouse for input. Mobile devices and tablets mainly use the human finger for input.
Yes, sometimes bigger computers have a trackball and laptop users also often use a trackpad for input. And there are even a few mobile devices that come with a stylus. But mice and fingers are the main input device for currently popular user interfaces. So let's consider their differences.
In the following table, green cells indicate the pointing device that is superior for each of the dimensions rated.
| Mouse | Fingers | |
|---|---|---|
| Precision | High | Low (“fat-finger problem”) |
| Number of points specified | 1 | usually 1 2–3 with multi-touch |
| Number of controls | 3: left/right button, scroll wheel | 1 |
| Homing time? | Yes | No |
| Signal states | Hover, mouse-down, mouse-up | Finger-down, finger-up |
| Accelerated movements | Yes | No |
| Suitable for use with huge screens (30-inch or more) |
Yes, because of acceleration |
No: arm fatigue |
| Visible pointer/cursor | Yes | No |
| Obscures view of screen | No, thus allowing for continuous visual feedback | Yes |
| Suitable for mobile | No | Yes: nothing extra to carry around |
| Ease of learning | Fairly easy | Virtually no learning time |
| Direct engagement with screen and "fun" to use | No: an indirect pointing device | Yes |
| Accessibility support | Yes | No |
Some notes for the table:
- Homing time is the time required to move the hands from one input device, such as the keyboard, to another, such as the mouse.
- Accelerated movements are the ability to have a non-linear relationship between the speed of moving the pointing device and the on-screen pointer: moving the mouse fast makes the on-screen pointer move even faster. Conversely, moving the mouse slowly makes the pointer move very slowly, allowing for high-precision pointing.
- When I say that there's virtually no learning time required to operate a touchscreen by pointing a finger, I am assuming that users have already acquired sufficient dexterity in using their hands and fingers. This does take babies a few years.
The main takeaway from the table is that there is no single winner. Mice and fingers each have their strong points.
When designing a user interface for a given platform, it's important to emphasize the strengths of the available input (and output) devices and also work alleviate their weaknesses.
For example, because the mouse has a hover state, tool tips and other roll-over effects can often be used to good effect on desktop computers. Similarly, contextual menus are easily supported by the two-button activation controls. These design elements are less natural on touchscreens.
The fact that the mouse and touch input have so different strengths is one of the main reasons to design different user interfaces for desktop websites and for mobile sites. (And also for desktop applications vs. mobile apps.)
Further arguments for two UIs are provided by the presence of a real keyboard on the desktop (making typing much faster and less error-prone) and the vast difference in screen sizes.
