A scrollbar is an object in a graphical user interface (GUI) with which continuous text, pictures or anything else can be scrolled including time in video applications, i.e., viewed even if it does not fit into the space in a computer display, window, or viewport. It was also known as a handle in the very first GUIs.
Scrollbars are present in a wide range of electronic devices including computers, graphing calculators, mobile phones, and portable media players. They usually appear on one or two sides of the viewing area as long rectangular areas containing a bar (or thumb) that can be dragged along a trough (or track) to move the body of the document as well as two arrows on either end for precise adjustments. The "thumb" has different names in different environments: on the Macintosh it is called a "scroller"; on the Java platform it is called "thumb" or "knob"; Microsoft's .NET documentation refers to it as "scroll box" or "scroll thumb"; in other environments it is called "elevator", "quint", "puck", "wiper" or "grip". Additional functions may be found, such as zooming in/out or various application-specific tools. The thumb can also sometimes be adjusted by dragging its ends. In this case it would adjust both the position and the zooming of the document, where the size of the thumb represents the degree of zooming applied. A thumb that completely fills the trough indicates that the entire document is being viewed, at which point the scrollbar may temporarily become hidden.
Scrollbars can be seen as a computer representation of a thumb, with which you thumb through pages of documents.
A scrollbar should be distinguished from a slider which is another object that works in a similar fashion, the difference being that the slider is used to change values, and does not change the display or move the area that is shown.
While dragging the thumb is historically the traditional way of manipulating a scrollbar, a scroll wheel may also be used. In addition, the arrow buttons may be clicked to scroll a small amount, or the trough above or below the thumb for a larger amount. Sometimes, both arrow buttons appear next to each other for quick, precise manipulation without having to drag the thumb or move the mouse great distances to the other arrow (this was offered as an option in Mac OS 8.5); one of them may also be duplicated so as to show at both ends of the bar, providing familiarity for those used to both separate and adjacent buttons.
Another system for manipulating them is to look at which mouse button was pressed. For instance, a left-click might cause it to scroll down, while a right click would scroll up, and the middle button could be used to place the thumb precisely. This form requires less fine motor skills, although it requires a multi-button mouse, and possibly a greater degree of GUI literacy.
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