I was really annoyed in not being able to connect a second monitor up to my MacBook Air in a configuration that pleases me.  I have a large screen Samsung (P2570) monitor that accepts HDMI and digital inputs.  (Note: if you have a HDMI TV, this method should also work.)  I purchased a Belkin Mini DisplayPort to HDTV Cable, 6 feet long (F2CDO3yw2M-APL exclusive to Apple Store).  It connected directly to my MacBook Air and the Samsung monitor.  I like to position that larger screen over and behind my laptop screen.  Problem for me was I could not figure out how to slide content from the MacBook Air up to the second screen.  Content would hit the edge of the laptop screen and stop.  I finally found the solution which is most interesting.

Aside:  I have a five year old MacBook Pro computer.  I always use extended desktop with that computer.  I found some slight problems with this older unit.   The computer seemed to remember the last location for that screen when you launch it next time.  This was a problem if I disconnected the second screen.  Application screens that were in that second screen could not be found because they were sent to the monitor that I had disconnected.  The solution was simple.  I would reconnect the second monitor and move content back to the laptop  or turn on mirroring and fix the problem.

I wanted to see how the MacBook Air handled this problem.  I tested this MacBook Air by putting application screens up to the second monitor, turned off my laptop and disconnected the second monitor and see what would happen.  I expected to NOT find missing content that was sent to the second monitor that I had just disconnected.  Apple really improved the software, boy have they!  My laptop reverted to single screen perfectly showing application screens that were positioned in the second extended desktop!  Wow!  I now leave my laptop configured for two extended screens and I only need to remove my laptop with no ill effects.  All the content that I left in the second monitor space would drop back into the laptop screen.  That is really cool.

Next, I will describe how to make the necessary changes to make a second monitor extend the laptop presentation.  My configuration is vertical with the second add on display over or on top of the laptop screen.

Method:

• Open System Preferences and look for Displays.  Open Displays.

• Turn ON “Show mirroring options in the menu bar when available”.  This really is not necessary.  I just like doing it in case I do not see all my content and need to fix that problem fast.

• Turn OFF “Mirror Displays”.  Mirror is when you want both screens to show the same thing, exact same content.  This method that I am describing is showing how to extend the laptop screen into a second monitor.  We will be increasing your viewing space by adding a second monitor that can show MORE content.  For example, when writing I like to always show the dictionary, web browser, and Pages or Scrivener.  That just will not work with the MacBook Air screen.  Laptops have small screens.  I put items into the second monitor screen.  This makes for a very efficient writing process.  I also love this method for composing my web pages.  I compose my text using Pages.  I have Adobe Lightroom open to find and manipulate photos.  I have a web browser open to check the look of my web content.  I have Grab open to capture screen content.

• Choose “Arrangement” tab so you can slide the displays around.  You can slide the second monitor left, right bottom or top of the laptop screen.  I chose top.

Typically the MacBook Air will be the smaller blue box with a white bar on top (see image below).

 

This is the trick method.

• Grab ONLY the white bar that shows on top of the laptop (small) blue box and slide it on top of the large second monitor box.   Actually it is important to slide the white bar into the second monitor blue box until that box shows a red outline.  That red outline indicates to you that the change will be made.  You naturally can slide that white bar back to the smaller laptop screen at any time.

 

In the above image you can see the white bar being moved (mouse cursor missing from image) from the lower blue box (laptop) to the larger and upper blue box which represents the second or added monitor.  Take note that the upper blue box is showing a red outline which indicates that the menu bar will now be a part of that monitor.  The image below shows the result.

Notice in the image above that I now have slid the white (menu) bar to the top of the second monitor.

 

That is all you need to do.  I found this setup worked perfectly.  Except, you will still have your task bar to launch applications at the bottom laptop box but your screen menu now is at the top of the second and larger second screen.
Now this makes sense.  We just made both screens a pillar of sorts with launch dock at the bottom of the laptop screen and the top of the displays extending up to the larger screen and the menu now resides at the very top of the second display.

A slight annoyance was that I had to move the mouse cursor up and down this huge vertical space over and over.  With the MacBook Air the track pad is very efficient and I figured I did not need a mouse.  I just might have to now to make the huge cursor moves easier.