Introduction
The scroll bar has become so commonplace that most users never notice it unless it's missing. Like the desktop metaphor, scroll bars are just a part of life. But for the clueless or the curious, it is worthwhile to look a little more closely at the ubiquitous scroll bar. What follows is a brief description of its usage and its history.
Usage
A scroll bar (sometimes written simply as scrollbar) is used to provide one way of navigating through a large document. If the document cannot conveniently fit into a single viewscreen (such as a browser window), often a scroll bar will be added. This scroll bar partitions the document into an "active" area, and the two "inactive" areas above and below the active area. Only the portion of the document that is currently active will be displayed to the user, and the scroll bar includes some mechanism for moving the active area, to enable viewing all parts of the document (but never all at once, of course).
The scroll bar is typically rendered as a vertical bar at the edge of the document1, with another bar inside it indicating the active area. The scroll bar always fits on the screen, otherwise what would be the point? The scroll bar's active-area indicator moves proportionally to the document's active area; e.g., moving the scroll bar's active area by 10% of the scroll bar's total length will move the document's active area by 10% of the document's total length.
The scroll bar can usually be moved in several ways:2
- By dragging the scroll bar's active area to a new position
- By clicking on the up or down arrows at its ends. Not all scroll bars have these buttons.
- By clicking an unoccupied area on the scroll bar. This usually results in the active area moving by approximately half of a viewscreen, in the direction of the click.
- By scrolling the document in some other way, such as with the arrow keys or the mouse's scroll wheel; the scroll bar is two-way synchronized with the viewscreen.
History
The scroll bar came into being at around the same time the other components of the window metaphor did. It is a very useful tool for handling large amounts of data, and will probably be with us for a long time.
Because the scroll bar is so ubiquitous, little thought is given to its name. Some terms, like folder, desktop, window, and so on, are so similar to real-world objects that we know immediately what their names mean. But the scroll bar's meaning is subtle enough that it doesn't jump right out at us. In fact, the term "scroll bar", in addition to the verb "scroll", both derive from the noun "scroll". The connection is not immediately obvious, but imagine having an actual scroll in your hands. The top end is rolled up a bit, and so is the bottom end, and you're looking a conveniently-sized section in the middle. If you want to read an earlier part, you can roll up the bottom further, and unroll the top, effectively moving your "active area" by a few inches (or centimeters). The scroll bar in a document is an echo of this scroll-rolling. So next time you're using a scroll bar (which is now), try to think of it as an actual scroll. It's a fun example of the metaphors we take for granted.
1 Horizontal scroll bars exist as well. They are a
trivial extension of
vertical scroll bars.
2 This list is not
complete, because anyone can write a new scroll bar that behaves oddly. But most
mass-market scroll bars act roughly like this.