Almost one in five households in Britain has at least two computers and many of them have both laptops and desktops. On top of that, a large number of people also own iPhones, iPads, or iPod touches.

Put those numbers together, and you have a lot of people who’d like to connect from one Mac (or iOS device) to another – whether that other computer is down the hall or across the country.

We need more than access to remote files. We also need control over the distant machine – to see what’s on its screen and to run its programs.

Fortunately, there are many ways to remotely access a Mac. They fall roughly into five categories:

1. Tools built into OS X itself, including Screen Sharing and Back to My Mac;

2.Chat services such as iChat and Skype;

3. Dedicated online services, including LogMeIn and GoToMyPC;

4. The dedicated remote control program Timbuktu Pro;

5. Tools based on the generic, cross-platform VNC (Virtual Network Computing).

(Remote Login using SSH isn’t in that list because it’s a pretty specialised tool; chances are, if you need to connect that way, you already know it – and know how to do so.)

Overcoming hurdles
Remotely controlling one Mac from another within the same local network isn’t hard; Bonjour and other networking tools make it reasonably simple. Controlling a machine on a remote network is trickier because much of the networking hardware and software that lies between you and the other machine is there specifically to prevent that kind of access.

One of the biggest barriers to remote access is that to control any remote machine, you need to know its network address. Home networks typically deploy two technologies – Network Address Translation (NAT) and Dynamic Host Configuration Protocol (DHCP) – that hide those addresses from view. Some remote-access tools (including Back to My Mac, GoToMyPC, and LogMeIn) take care of this problem by talking directly to a router’s NAT software, in order to establish specific paths into the network.

Other solutions (including OS X’s built-in Screen Sharing software and VNC) require that you set up port mapping – establishing persistent connections between ports on the router’s internet-facing IP address and specific computers inside the network.

If you’re lucky, NAT Port Mapping Protocol (NAT-PMP, favoured by Apple) or Universal Plug and Play (UPnP, common on non-Apple hardware) on your router can take care of the port mapping for you. Third-party software such as Port Map (free, www.codingmonkeys.de/portmap) or Lighthouse ($12.99 [£8], www.codelaide.com) can also do the trick. You can map ports manually, but you have to know which ones are used for which services, how to assign persistent addresses, and how to find your external public IP address. One other solution to the “Where is my computer?” problem: Dynamic DNS, which lets you map a human-readable domain name, such as remote.mymachine.com to your router’s public IP address. For more on how to do that, see “Setting Up Dynamic DNS” (www.macworld.com/6439).

The right route
To figure out which remote-access alternative is right for your needs, you need to consider a few different features:

Security: all of the options mentioned here, except for VNC, strongly encrypt remote-access connections by default. If you opt for VNC, you need to take extra precautions.

Cost: the most reliable options cost the most. LogMeIn and GoToMyPC have hefty, recurring, per-machine subscription fees; Timbuktu Pro has a high, one-time per-computer price tag. Back to My Mac is less expensive (the cost of a MobileMe subscription), but it doesn’t work for everyone.

Multiple monitors: if the remote machine is connected to more than one display, can your remote control program show you all those screens?

File sharing: surprisingly, many remote control programs offer no good way to move files from one computer to the other.

To help you decide which remote control option meets your needs, we will walk you through each one – its pros and cons, and the ease (or difficulty) of setting it up.

Remote systems appear in the Shared section of the Finder sidebar

Built-in Tools
Two of the simplest ways to access another Mac are built into OS X: Screen Sharing and Back to My Mac. OS X 10.5 (Leopard) and 10.6 (Snow Leopard) both come with the robust Screen Sharing program. It lets you access other 10.5 and 10.6 systems, and it’s compatible with the industry-standard VNC protocol. However, Screen Sharing alone is best for connecting to computers hooked up to the same router. But when paired with Back to My Mac, Screen Sharing becomes much more powerful, if you have a MobileMe account.

Screen Sharing manages multiple monitors relatively well. If you enable File Sharing on the remote system, you can transfer files over the same connection.

Assuming you have a MobileMe account, you enable Back to My Mac in the MobileMe preference pane. On the pane’s Back to My Mac tab, click Start to activate the service; a green dot appears when it has registered your computer. Turn on Screen Sharing (in the Sharing preference pane) on the systems you want to access remotely. Once active, any remote computers registered to the same MobileMe account should appear in the Shared section of the Finder sidebar.

To access one of those computers, select it from the sidebar list and then click the Share Screen button. If the remote system has the same OS X username and password as the computer from which you’re connecting, you may not even be prompted to log in. Once the connection is made, you can scale the screen, adjust screen quality (to reduce the bandwidth required), and choose to see one or all of the remote monitors.

If Back to My Mac isn’t working, open its tab in the MobileMe preference pane. If you see a green dot for connection status, click Stop, wait, and then click Start. If you see a yellow or red dot, check out “Troubleshooting Back to My Mac” (www.macworld.com/6440).