Operating Systems Introduction
Author: Brian Brown, 1995-2000. All rights reserved.
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Basic Features of Graphical Interfaces
Graphical systems use windows to display information and thus
allow more than one window to be displayed at any time. Each
window is associated with a running program. User input is
derived from a keyboard and mouse.
The mouse
The mouse, invented in 1963 at the Stanford Research Institute by
Douglas Engelbart, has done much to enhance the use of the
personal computer. Engelbart's prototype, made of wood, with
metal disks for rollers that detected the motion of the mouse,
was further developed by Xerox at it's Palo Alto Research Center
in the early 1970's under the direction of Jack S Hawley.
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Most mice have two or more buttons, which users depress to select items from a menu or click on graphical objects on the computer screen, thus sending commands to the computer. |
The mouse is held in the hand and moved across a flat surface. As the mouse is moved, its movement is detected and translated into both X and Y movements, which updates the indicated position of the mouse pointer on the computer screen accordingly.
The mouse cursor
The position of the mouse is shown on the screen as the mouse
cursor and is denoted by a number of symbols.
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Standard mouse pointer |
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Indicates computer is busy |
Selecting items with the Mouse
Single Click
A single mouse click refers to moving the mouse pointer over the
desired item and quickly pressing the left mouse button once.
Double Click
A double mouse click refers to moving the mouse pointer over the
desired item and quickly pressing the left mouse button twice in
rapid succession.
Drag
A drag or move operation is performed by moving the mouse pointer
over the desired item and holding the left mouse button down. The
mouse is then used to move to drag the object or window to the
new position, then the left mouse button is released.
Window Fundamentals
In a graphical operating system, information is represented in
graphical ways. Little symbols or pictures (called icons) are
used to display programs or information. Information is displayed
inside windows, each of which has similar properties.
It is possible to have more than one window on the screen at one time, and windows may be cascaded (on top of one another) or tiled (all displayed at once and all visible).
In this picture, the windows have been cascaded. This makes each window appear on top of each other, one after the other. The front most window is considered to be the active window, ie, the window to which the users commands will be sent. In Windows95 or WindowsNT, the titlebar of the window is shown in the default color Blue. |
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In this picture, the images have been tiled. This makes all windows visible at the same time, but resizes the dimensions of each window so that they all fit on the available screen space at once. |
Tip: To cascade or tile all windows on the desktop area, right mouse click on an empty portion of the taskbar and select Cascade Windows or Tile Windows from the menu.
Window Properties
Each window has the same properties and behaves the same way.
This provides a consistent interface to the user, as all commands
are the same for each window and the operations that the user
performs on each window are identical.
In the diagram below, we see the basic window as presented by Windows 95 or Windows NT. Each property is listed on the diagram, and below is an explanation for each of the window components.
The Title Bar
This normally displays the name of the program associated with
the window. If the background color of the title bar is blue, the
window is active and any user commands will be processed by that
window. You can also toggle between a maximized window size and
the windows normal size by double clicking in the title bar area.
The Control Menu
Clicking on the Control Menu pops up a small Window of selectable
options, which include the operations of Restore, Move, Size,
Maximize, Minimize and Close the Window.
The Horizontal and Vertical Scroll Bars
When the amount of information displayed in the window exceeds
the viewing space of the window, scroll bars are automatically to
the side and bottom of the window. This allows the user to scroll
the contents of the window in order to view the remaining
information. Arrows are used to indicate the direction of
scrolling on the scroll bar, and an indicator bar represents the
relative position of the viewing area compared to the total size
of the information.
Clicking on the arrows associated with the scroll bar move the viewing window up or down one line, or across or back one character position. You can also click on the small indicator bar within the scroll bar and drag it with the mouse to quickly scroll the windows contents.
The Minimize Maximize Close Window Buttons
These buttons are located on the top right corner of each window.
Clicking on them once performs the desired action associated with
the button.
reduces the window and
places it on the taskbar at the bottom of the window.
expands the window to fill
the entire desktop screen area.
closes the window.Tip: To minimize all windows on the desktop area, right mouse click on an empty portion of the taskbar and select Minimize all Windows from the menu.
| The Menu Bar
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The menu bar presents a number of
options that the program associated with the Window
supports. Clicking on an option on the menu bar will popup a submenu of choices that you can select from. |
The Windows Borders
The windows borders show the dimensions of the window. Any window
can be resized, either made smaller or larger, by dragging the
window border appropriately.
, then hold the left mouse
button down and drag the window border to its new
position, then let release the left mouse button.
, then hold the left mouse
button down and drag the window border to its new
position, then let release the left mouse button.
Moving a Window
A window can be repositioned on the desktop screen display area
by moving the mouse cursor into the title bar area, then holding
the left mouse button down and dragging the window to the new
position, then releasing the left mouse button.
Switching between Windows
When you have multiple windows displayed on the desktop screen
area, you can switch between windows by clicking on the programs
icon on the taskbar or pressing ALT-TAB keys on the keyboard.
When you press ALT-TAB, it will pop up a window of the available
programs. Hold the ALT key down, and pressing the tab key will
move the selection to the next window in the list. When the
desired window is highlighted, release the ALT key and that
window will become active.
Clicking on the applications icon on the taskbar can also do switching to another application. The following picture shows the Windows taskbar, located at the bottom of the screen.
| This picture shows the ALT-TAB pop up window, which list the available programs the user can switch to. |  |
