I remember the first time I used a remote screen-sharing program. Working from my desktop computer, I accessed a system that was in a server room but which had no monitor attached. It was magical. I could work with the server just as if I were directly connected with a keyboard and mouse, using its programs and manipulating objects on its desktop, but I didn't need to sit in the server room and have the inconvenient extra hardware attached to the server.

That sense of wonder still pervades me when I use screen sharing 18 years later. Instead of using a 10 Mbps (fast!) local Ethernet network or 2,400 bps dial-up software to make the connection, I use broadband feeds over the Internet to reach computers across town, 15 miles away, and 3,000 miles away.

Screen sharing gives you access to applications and data stored on another computer, even though your keyboard and mouse aren't connected to that computer. It also gives you the freedom to switch between computers in different locations without using individual remote-control applications, most of which are wonky or slow when used over the Internet.

Leopard extends the use of screen sharing from something you had to install or figure out how to use in Mac OS X 10.4 Tiger and earlier versions of Mac OS X to being part of the system, available on tap.

In Leopard, screen sharing comes in several forms, each of which I explain how to use in this book. In some forms, you need to be in control of each machine you want to access remotely, having an account and password on that computer. However, one particular method—Screen Sharing over iChat—requires just a buddy who gives you permission to access his or her screen.

I also cover VNC, a technology that's built into many different programs for many versions of Mac OS X and other platforms, and which is the basis of much of Leopard's screen-sharing capability.