2 monitors, 1 image
This is the most common and probably simplest setup. When a teacher has their laptop set up to display on a projection system this is typically what we see. The same image is displayed on the laptop (or desktop) screen and on the projector screen. For doing demos or showing how to navigate a website this is a very useful setup. It also is usually the default system configuration so it requires very little adjustment by the teacher. But what if I want to to do more?
This feature is referred to as 'cloned' monitors on Windows and 'Mirroring' on Mac
2 monitors extended display
Sometimes though, you want to be able to multi-task. For example. Maybe I use PowerPoint for my bell ringer activities. I want the students to see the PowerPoint slide but I need to take role? What's a teacher to do? Typically, we would either have to have two computers one for presenting and one for administrative tasks, but there is a simpler way. If you turn off 'cloning' or 'mirroring' you get a larger desktop. When your computer is connected to a projector that display becomes an extended desktop (That's the PC term, and I don't mean politically correct) With programs like PowerPoint this enables features that let you display the slide show on the second monitor while leaving the laptop (or main desktop) screen free to do other things like take attendance.
3+ Monitors means true multitasking.
With the adoption of new computers, often laptops, the older CRT monitors are sometimes surplused out of existence, but if you have an older CRT monitor or even better an LCD monitor and a laptop, (or really any computer) you can really start to dazzle. One configuration that I used and loved was to buy a VGA Splitter and send the image from my laptop to 3 places. I usually extended the desktop to the "second" display which was really the splitter. The splitter then boosted the signal and sent it to a second monitor on my desk and to my projection system. This let me not only see my own screen, but also see the PowerPoint slide the students were seeing behind me. When I needed to do a demo, it was just a couple of quick clicks of the mouse to switch back to cloned mode and I was ready to show students how to create a chart in a spreadsheet. I would see the same image on my two monitors that they saw projected behind me.
With Windows Vista and Windows 7 you can really do even more and extend the desktop onto multiple monitors. This may mean an additional graphics card or some specific technical help, but you can have up to 10 monitors connected to one computer. If you are the kind of person who has email, calendars, web, grading, and Instant messaging all going at the same time, this could be a really good solution for you.
To see what Microsoft is saying about Multiple monitors Click here.