A window in a Microsoft Windows application can display a data object, such as a document or a bitmap, that is larger than the window's client area. A scroll bar represents the overall length or width of a data object in a window's client area. It lets the user shift the data object in the client area to bring into view the portions the object that extend beyond the borders of the window. Shifting the contents of the client area is called scrolling. You should include scroll bars in any window that can be sized such that the contents of the client area extend beyond the window's borders.
You can include horizontal and vertical scroll bars in your application's windows. A scroll bar's orientation determines the direction in which scrolling occurs when the user interacts with the scroll bar. A horizontal scroll bar lets the user scroll the contents of a window to the left or right. A vertical scroll bar lets the user scroll the contents up or down. The following illustration shows horizontal and vertical scroll bars in the Windows Write application: