Mouse Button - Operating System Use

Operating System Use

The Macintosh user interface, by design, always has and still does make all functions available with a single-button mouse. Apple's Human Interface Guidelines still specify that all software-providers need to make functions available with a single button mouse. Context menus are available using the Control Key ctrl.

The original Mac OS assumed a one-button mouse. While there has long been an aftermarket for mice with two, three, or more buttons, and extensive configurable support to complement such devices in all major software packages on the platform, Mac OS X shipped with hardcoded support for multi-button mice. X Window System applications, which Mac OS X can also run, have been developed with the use of two-button or even three-button mice in mind.

Advocates of multiple-button mice argue that support for a single-button mouse often leads to clumsy workarounds in interfaces where a given object may have more than one appropriate action. One workaround was the double click, first used on the Apple Lisa, to allow both the "select" and "open" operation to be performed with a single button. Several common workarounds exist, and some are specified by the Apple Human Interface Guidelines.

One such workaround (that favored on Apple platforms) has the user hold down one or more keys on the keyboard before pressing the mouse button (typically control on a Macintosh for contextual menus). This has the disadvantage that it requires that both the user's hands be engaged. It also requires that the user perform actions on completely separate devices in concert; that is, holding a key on the keyboard while pressing a button on the mouse. This can be a difficult task for a disabled user, although can be remedied by allowing keys to stick so that they do not need to be pressed down.

Another involves the press-and-hold technique. In a press-and-hold, the user presses and holds the single button. After a certain period, software perceives the button press not as a single click but as a separate action. This has two drawbacks: first, a slow user may press-and-hold inadvertently. Second, the user must wait for the software to detect the click as a press-and-hold, otherwise the system might interpret the button-depression as a single click. Furthermore, the remedies for these two drawbacks conflict with each other: the longer the lag time, the more the user must wait; and the shorter the lag time, the more likely it becomes that some user will accidentally press-and-hold when meaning to click. Studies have found all of the above workarounds less usable than additional mouse buttons for experienced users.

While historically, most PC mice provided two or three buttons, only the primary button was standardized in use for MS-DOS and versions of Windows through 3.1x; support and functionality for additional buttons was application specific. However, in 1992, Borland released Quattro Pro for Windows (QPW), which used the right (or secondary) mouse button to bring up a context menu for the screen object clicked (an innovation previously used on the Xerox Alto, but new to most users). Borland actively promoted the feature, advertising QPW as "The right choice", and the innovation was widely hailed as intuitive and simple. Other applications quickly followed suit, and the "right-click for properties" gesture was cemented as standard Windows UI behavior after it was implemented throughout Windows 95.

Most machines running Unix or a Unix-like operating system run the X Window System which almost always encourages a three-button mouse. X numbers the buttons by convention. This allows user instructions to apply to mice or pointing devices that do not use conventional button placement. For example, a left-handed user may reverse the buttons, usually with a software setting. With non-conventional button placement, user directions that say "left mouse button" or "right mouse button" are confusing. The ground-breaking Xerox Parc Alto and Dorado computers from the mid-1970s used three-button mice, and each button was assigned a color. Red was used for the left (or primary) button, yellow for the middle (secondary), and blue for the right (meta or tertiary). This naming convention lives on in some Smalltalk environments, such as Squeak, and can be less confusing than the right, middle and left designations.

Acorn's RISC OS based computers necessarily use all three mouse buttons throughout their WIMP based GUI. RISC OS refers to the three buttons (from left to right) as Select, Menu and Adjust. Select functions in the same way as the "Primary" mouse button in other operating systems. Menu will bring up a context-sensitive menu appropriate for the position of the pointer, and this often provides the only means of activating this menu. This menu in most applications equates to the "Application Menu" found at the top of the screen in Mac OS, and underneath the window title under Microsoft Windows. Adjust serves for selecting multiple items in the "Filer" desktop, and for altering parameters of objects within applications – although its exact function usually depends on the programmer.