I remember when Windows 98 introduced the ability to support multiple displays. If you had a desktop system with room for multiple video cards, you could have multiple monitors. This was great for those of us who ran way too many applications at once—you could split your workspace between multiple desktops. Since that time, video chips have gotten more powerful and can now drive multiple displays with a single chip.
Apple’s iMac and MacBook lines feature an internal display as well as a port to connect an external display. The displays can be configured to run the same desktop on both (which comes in handy for presentations), or two different desktops. With a USB to VGA adapter, you can add a third display, but it won’t be very fast. The Mac mini has no built-in display, but has adapters for two external displays—Mini DisplayPort and HDMI—and could potentially drive a third display with the USB adapter.
With the introduction of Thunderbolt, it is now possible to have multiple displays on any system that has a Thunderbolt port. The 15” and 17” MacBook Pro systems can support two Thunderbolt displays connected in a chain. The 13” MacBook Pro can support a total of two displays, whether they be the internal plus one external, or two externals. (Plugging in a second external display disables the internal display.) The MacBook Air can drive one external display.
According to Apple, if you have multiple Thunderbolt devices, the Thunderbolt Display should go first, then any other devices like a hard drive should be connected to the Thunderbolt Display. Putting the display last in the chain affects data throughput of the other devices.
You can daisy chain a Thunderbolt display with an Apple CinemaDisplay, or any other display that uses a Mini DisplayPort connection. You just have to put some other Thunderbolt device between them. Connecting the CinemaDisplay directly to the Thunderbolt Display does not work.